My Mom (88) with dementia, has a 65 yr old man with Alzheimer's that keeps going in her room and licking the door. What can I do?

Somehow I find it reassuring that he is locking the door instead of licking it. Sorry, the image of licking was too much.

One of the things they ask when a patient is first admitted is whether they are "consenting" or "non-consenting" which is a polite way of asking about sex.
If she is designated as non-consenting, Mr. Lick is in trouble, you file a complaint and he gets moved to memory care.
If she is consenting, well they can have all the fun they want. Make sure you clarify her status with the Head Nurse (no pun intended).

Sorry, it is locking not licking.

The nurses that take her meals and medicines have tried to go in to do so and have to get her to unlock the door and he will be on her bed. He got mad at the nurse and said she couldn't go in my moms room without knocking. They do knock wait a minute then go in. He is getting possessive of her.

I was thinking the same thing! Yew!!!!!!!!

Licking the door?! I thought what in the world, but with dementia you never know! LOL!

I am curious, does Mom invite him in? If she enjoys his company, there should not be a problem. They must be in assisted living? Does Mom have dementia? If so, you need to keep an eye on things, but be careful so you don't hurt her feelings or make her mad. If she is competent there should not be a problem with this visitor.
You mention Mom's and his ages. That would not make a difference to me. And I would think it nice that she has this friend.

nh romance .
i get tickled sitting in ednas nh lunchroom checking out the old gals and trying to imagine them when they were young and possibly promiscuous . the looks they give me back tells me they know what im thinking . the old gal is thinkin " dam , if i were 20 yrs younger " n im thinkin " dam , if it were dark in here " ..
then i go back to the ac dc blaring in my head ..

I read "licking" and thought, "I've got to get in on this conversation!"

Now I am puzzled. Your profile says you are caring for Mom at your home and that she has dementia. Maybe Mom should be in memory care? That way the staffing ratio is lower and she will have her care needs met.

If she has dementia, she cannot "consent" to sex, so forget that angle.
Tell the staff about the problem, and that you don't want him in her room. Document it in writing to the administrator. They have to manage it.
Take the lock off the door, and yes, she shouldn't have any valuables. If she's not in her right mind, door locks could be dangerous anyway, esp. if the staff doesn't have keys, which it sounds like they don't since they have to ask her to open the door.