My 83 father-in-law (severe dementia) who lives with us is a major fall risk. He constantly roams the house in the middle of the night and likes to hang out on the stairs. As a matter of fact, yesterday morning around 5:00 am, we heard a crash and woke up to find he had fallen and busted his eye (completely black now) and skinned his left arm so badly that we had to bandage his entire arm. He's also on blood thinners, so even minors falls end up looking and feeling far worse. By the time he wakes up in the morning, he forgets he fell and argues that he never falls. We actually have cameras all over the house for him for this purpose. Any tips?
You can place his mattress on the floor. Granted you will have to help him get into and out of bed but the risk of falling is minimized. (If you go this route a Hoyer Lift would be the easiest and safest way to get him up and down)
A Hospital bed at it's lowest position might help. And since this is your home and not a facility you can use bed rails. (Not permitted in facilities as it is considered "confinement")
Stop arguing about it. There is no "winning" an argument with someone that has dementia. He will not remember that you told him not to get up, he will not remember that he got up, he will not remember how he fell or if he fell.
Unfortunately the possibility is high that at some point he will fall and break a leg, arm, hip or concussion that will hospitalize him. Rehab would be the next step and I doubt he would be a candidate for rehab. (sorry to be so blunt)
You can use motion or bed alarms to let you know when he's getting up and I would consider some significant gate to barricade the stairs. Reaching the wandering stage of dementia is also the point at which many families begin looking into LTC because it's so difficult to provide the same level of 24/7 supervision a facility can.
Good luck!
This is going to get worse and the next fall could kill him. He needs more monitoring and help than you can give. Please consider memory care?