I am having trouble convincing my husband with Alzheimer's that we live in our home. We have been living here 21 years this summer. Advice?

My response doesn't help the core issue but I think you might want to think about the wandering issue. I believe that there are devices that you can sew into his clothing that can be monitored so he can be found more easily. If you can get him to wear an ID bracelet that would also help. When I travel out of my state, I wear an ID bracelent that has contact information in case I am in an accident or require medical care.

I’ve heard it is common for people with Alzheimer’s & dementia to want to go “home”. My mother was concerned for many years about going “home”. I finally figured out home wasn’t a location, it was a feeling of security she had as a child with her parents. So when she would want to go home, even though she was in her home of 30+ yrs, I talked about her mom & dad & how much they had loved her & told her everything is ok & we’re going to have lunch in a bit, or go get an ice cream cone (just anything positive to distract her & make her insecurities subside) & she felt better. Car rides & ice cream cones helped for years. The dogs came along & fast food cones barely cost anything. Then when we got closer to her house, she could point the way when I would ask where home is, she was right & we went home to reset. But “home” is a state of mind, they feel lost. Reassurance, happiness & redirection was our go to for a long time. She eventually got past it as the dementia advanced.

Your father's constant urge to "go home" is not necessarily a physical building, but in fact going to a place where he felt secure and loved, and where someone took care of him. Of course, he may well have romanticized the beauty of it all.
Why are you falling into the same loop that your husband is in?
Don't be lured into making sense to someone who cannot make sense himself.
"No dear, everything is just fine. We are staying here for now," then remove yourself from the repetition. The assurance that everything is OK is what he's looking for.

He is mentally gone forever - things will get worse and worse and worse. It is time to fax the fact he must be "contained" in a place of safety and that means getting him out of your premises and placing him. You have no choice. You must protect yourself and YOUR sanity.

My 'go to' answer for any question my husband asked (when I knew the truth would not satisfy him) was "your guess is as good as mine". It worked for him and helped me hang on to a little sanity...( He is now at an AFH and I wish he could still ask a coherent question...going downhill fast, but getting better care that I could give)

ONE ANSWER: "Let's get a chocolate shake" (malt or ice cream). whichever they liked as a child!
The diversion worked every time! He is now is a Care Home and I still take him for a drive (or bring him) a chocolate shake--he's immediately home!