My dad is planning to run away from home. What can I do to stop him?

He seems like he is passed Independent Living. He needs Memory Care.
The fact is in Independent Living they can not stop him from leaving. He could very well "wander out" at night to go for a walk, go to the store, or anywhere he pleases.
If you, the family does not wish to move him to Memory Care then part of this is on you. Yo can place a "tracker" on phone, in his wallet or other piece of clothing. At least that way you can tell where he is. Some you can set to a particular range so if he leaves the area you will be notified.
But the only way to prevent him from leaving is to transfer him to a locked MC unit.

Based on your comment, "His last trip was an excursion on a 3 wheel single speed granny bicycle. He went 30 miles across a mountain on an unimproved road. He was found dehydrated, disoriented and spent several days in ICU. He claims no memory of the event.
This "trip", he asked a family friend for a ride. To my knowledge he doesn't know anyone at the destination. He is planning in secret and then just disappears without warning. We never know if he is in a ditch or on an adventure.
If he wants to travel, I don't begrudge him that. It's not fair that he leaves and worries everyone unnecessarily. Involving friends, neighbors and police in a silver alert/man hunt is terrifying."

You need to realize your father has more than 'mild dementia' going on, and nearly died on his recent 'trip' which you don't want to 'begrudge' him of. He does not have the mental ability to take these 'trips', to leave on his own, and if you continue to allow him to do so, he is going to die.

Dementia is a brain disorder; the brain no longer functions properly, as evidenced by his bicycle trip. Understand and believe this statement to be a fact. And, as such, treat it with the seriousness it deserves by placing your father in a Memory Care Assisted Living environment where he is unable to leave the premises.

Otherwise, his next trip may be to the morgue. I used to care for an elderly man with dementia who believed he lived across the street. His daughter 'loved him too much' to place him in Memory Care, and felt he was entitled to live in his own home & do as he saw fit. Which he was...........and he was also entitled to pay the consequences of his actions, I guess. Because one night, he left the house, fell in the street & wasn't found for a few hours. When he was taken to the ER by ambulance, he was too far gone to be saved. He had a subdural hematoma and died the next day.

Your father is not capable of taking a 700 mile trip. Do something to prevent it before it happens. Either that, or accompany him on this trip so you can care for him during it and make sure he's not doing something to endanger his life. He can't use reason anymore; dementia prevents it.

Wishing you the best of luck managing your father's care.

If he has access to a car, disable it completely ASAP. Make sure it is not something that can be fixed easily or cheaply. I agree he needs to be in memory care that is locked. I know that sounds harsh, but it is what I had to do for my Mother’s security. I was well advised she would not be safe in any facility that was not secured. I checked out a few before making the selection and it was quite nice and the best thing for her. She was free to walk around the facility wing. Walk out into fenced in courtyard, tv room and be apart of activities.

My brother in law and sister in law where moved to AL when their son felt their mental state was normal. It wasn’t. Wife’s Alzheimers state was worse then his, but he was in beginning stage of Alzheimers. On the 2nd morning, they did not show up for breakfast, so the staff checked up on them. Their car was gone. No cell phone. It was 2 days before they were found. Thankfully safe but confused.

When we lived in FL it was more then once a golf cart driver was found on Hwy 75 driving their golf cart in the lane of traffic, not knowing where they were.

Does he own a smart phone? If so you can install a tracking app so you at least know where he is (police can get some idea of his location by the last cell tower it pinged even if the phone is turned off... this also is true for an analog phone, like a flip phone)

Does he carry keys? You can put a Tile on it that will also track him, just don't tell him what it is.

The title of your post tugs at my heart, I can't imagine the worry you are feeling. Was he an adventurer in his younger days?

Seems it is time to make sure dad has round the clock care:

Home health aides can keep track of him round the clock - if there are finances available for this,

Residential facility - I'm thinking memory care unit - can also keep track of him. Most memory care units have different methods to keep their residents from fleeing.

Figure out why or where your dad wants to leave. Maybe he wants a trip to a specific location or he is tired of all the COVID restrictions. A short trip with a trusted family member may cure the desire to flee.

You got some good suggestions here (and some good questions. It might be that it is time for him to move to a secured (locked) MC unit in either an AL or a LTC provided he has be diagnosed with dementia. Not sure if finances are an issue but AL's generally do not have a lot of Medicaid beds so payment is private out of the individuals pocket. Many LTC facilities have secured units but you ideally want to have a unit that is certified. It means that the staff has to continuously take dementia related training and that the resident-staff ratio may be a little better.

In any event, trying to get placement anywhere in the midst of a pandemic is problematical so (without knowing where you live) I would suggest that you get in touch with your local Sheriff's Office and/or your state office on Aging to see if they have a monitoring program available. Mercer county in NJ has such a program and the tracking devices are available free of charge provided you have a verified doctor's diagnosis of dementia. The Office is run by the Sheriff's department. They come to the house, meet with the dementia patient and a family member, ask some questions, take a photo and then present the dementia patient with a lovely "bracelet" in honor of something they have made up. Thing is waterproof and goes on and doesn't come off without a special tool. Needs a new battery which they will come and replace every 60 days or so (my Mom used to look forward to their visits!). Although it has a fairly short range 3-5 miles, it has located a number of wandering folk here very quickly saving taxpayers, police and families a lot of worrying and anguish.

Your father has mild dementia now; but then you state that over the past ten years he has "run away from home a couple of times."

In what sense was he running away? Why wouldn't he have been willing and able to discuss these adventures with his family beforehand? I suppose I'm wondering why you can't just ask your father about his travel plans in the ordinary way.

Please get a second and third opinion on how to manage his pain because in my urgent earnest sincere honest experience , I have learned that medical management of humans health for the last 30 years has switched to using Petri dish corporate science, rather than doctor nurse, time tested, clinical, professional hands on, human health care . Once you get the health care team to switch to the root cause of pain, that’s when you’ll have a chance to stop the madness.

Get your dad to see a “functional medicine” doctor or do a virtual consult to start ASAP. Please. That’s what I did and my parents have zero pain now. No more leg and joint pain, no more hand arthritis pain, no more hip, back, foot pain ... nor more yo-yo diabetes blood sugar either and no more agitation from high blood pressure either and no more medication. Except for a little Metformin as insurance when my dad goes to parties or I can’t control the meals . No elder should be on a cocktail of drugs without a variety of health guidance and nutritional guidance. Food = Mood.
My mother also used to walk out the door . Once I got her to a doctor that knew the root cause of diseases, everything changed .
Or once I began to analyze first if the diet was optimal or not and his environment was engaging and fulfilling enough, then the meds are also addressed if not firstly.

Also get a male companion his age or younger disguised as housekeeper that will eventually begin chatting with your dad and get him to talk which will be a catalyst into doing other activities eventually.
what you can do in the meantime is calculate how much hydration he gets of “electrolytes” in his water and food choices. Check If he’s dehydrated (pinch the skin above his wrist and if it sticks together and doesn’t go back down fast, then he’s dehydrated) Buy super C or Emergecy C electrolyte drink at CVS and give half the dose to see if he calms down . You can also try CALM with calcium or by itself just CALM Magnesium but just 1/3 of the portion.
if you don’t have time to try these things which has helped too many people and elders and you can read about it in medical journals and the symptoms of dementia becoming unmanageable due to too many drugs and other lifestyle and nutrition factors.

Look online for the functional medicine practitioner website . Many MDs have switched to incorporating functional or integrative medicine into their practice but they might have stopped taking insurance because they focus or the root cause of disease instead of using drugs merely to stop symptoms .

Your profile says he is in independent living. If so, then what do you mean by "running away"? Do you mean he's planning a vacation? It's not the same thing but I understand your concern if he has memory issues or his decision-making is less rational. If he does not have a dementia diagnosis and you are not his legal PoA then you can't really stop him. How is he planning on traveling: by car or plane or someway else? Is he aware of the risks of covid? You'd need to talk to whomever will be hosting him at his destination to make sure he's safe.

If he forgets his medication would it be life threatening for him? Can you offer to go with him if he's really determined? How is he making the travel arrangements? Is someone there helping him? If you could provide more info it would help the forum participants to provide better suggestions.

It's so interesting that he is now planning this next trip in secret. I would interpret that as meaning he *does* remember something about his prior trip and that he has some understanding that this new trip must be kept quiet so it isn't thwarted. Is it possible he is suffering from some sort of mental illness rather than dementia? Based on his prior excursion that nearly did him it he seems like a candidate for MC.

When I was in 9th grade I remember a girl who was regularly called out of class so that she and her entire family could go search for her grandmother, who had dementia and lived with them, and would pack her suitcase and leave. No one was able to be home to care for her for a while. I remember the stress it caused this girl and her family.