Need "child" proof barrier to stairs for dementia client.

If the problem is only him going up the stairs and the layout allows, you could install a full or half door at the bottom of the stairs to prevent him from climbing the stairs. When I lived in a split level house, I installed a door at the bottom of the stairs and made the lower level into my "studio apartment".

I want to reiterate my gate solution cause I know it works.

The gate is attached to one wall with hardware. Don’t use pressure gates - they are useless in my opinion, even with toddlers.

Mount the gate at the first step. Mount the gate about knee level
at the point as if you were standing on the first step.

Im 5’8”. So, for me the gate would reach from my knees to my breasts. No one - even with dementia - is gonna think they can climb over it. As well, in the case of stairs going up - when locating the gate at the first step - the steps themselves will work as a barrier for any attempts to crawl under. Does that make sense?

This works. We have this set up in two houses. It works for either up or down. However, if you want it for going down steps it best to hang the gate at the landing/floor level rather than the first step. Make sense?

Additional helpful idea: In cases when someone spends a lot of time in their room - but needs supervision - replace the door with a typical screen door. This works too. Living with a severely- yet clever bugger with Autism for 26 years has forced my creative problem solving to new heights.

As an extra layer of security you could also use a motion or a pressure mat alarm to alert you when he is moving toward the steps.

Gates can be dangerous many people try to step over them and loose balance and fall, on a stair that is even more dangerous.
A dark rug as others have suggested might help.
If there is any way to place a full door at the bottom of the stairs that might also help. It would make things a bit more difficult for the wife.
If someone is with him at all times an infrared triggered bell might give you warning that someone is by the stairs. Many stores use these to alert staff that someone has walked in. There are alarms that normally go on a bed that could be placed on the floor and if anyone steps on it you or other caregiver will be alerted.

We had 2 sets of 4 grandbabies born within 5 month periods (does that make sense?) and we have a split entry home. DH installed a baby gate (and I cannot remember the name, but it was strong!) He didn't use the spring mount because all 4 of the babies would stand at the top of the stairs and shake that thing to death, knowing ALL the big kids were down where the fun was :) The secret was installing the gate into the wall and making it structural, rather than easily removable. It had a difficult latching mechanism which needed adult size hands to open. We left it up for years, even though it was a bit of a tripping hazard for adults. By the time the first set of quads were able to play downstairs, we had the SECOND set of quads. Left that gate up for 6 years. And it was tough!!

What Jessica said was true. We always wondered why Mom tried to walk over a dark rug we had.

There are baby gates that mount on the wall. Then it can be opened and closed when needed by someone else. If you go this way, like said mount it to waist high or more to prevent the person from trying to climb over.

With my Mom to prevent her from trying to climb over I put the gate one step up. I had a wall on each side. I was using a pressure gate. She never tried to remove it. Worked as a deterant/obstacle. It came with the brackets.

The poor lady. This was always a fear for me. Mom becoming needy. I can't stand turning around and finding someone right behind me. From early ages my girls and hubby too, knew not to come into my kitchen when I was doing something. Cats would be put out too. My husband has been almost deaf since he was 4. He teases me that he is getting ALZ. Being deaf is a criteria for Dementia. I just know if he developes it he will be following me around.

I've read that putting a black round rug (or any size) on the floor in front of the door helps because their depth perception is off and they think it's a hole so they won't go near it.  It might work for the stairs.  Worth a try.

When my MIL wandered we put an upholstered chair (on sliders) in front of the stairwell when she got up in the morning and moved it to its usual position when she went to bed. Worked almost all the time for us.

They are a little harder to find these days but look for a baby gate that mounts with hardware to one side of the wall - verses the type that are held in place by spring loaded pressure.

Then mount the gate roughly two feet off the first step. It will be impossible to crawl under or climb over.

As well, when you look for the gate check the dimensions. Some are longer from top to bottom than others. Get the largest one possible. I’d suggest looking on line for such a gate - they are hard to find in stores. The pressure gates are much more popular.

Trust me - this works. My disabled adult son is about 6’2” and has the longest legs ever. Rainman hates going down stairs but doesn’t fear going up stairs - the gate has worked for us.

Well, other than installing a locking gate at the top and bottom of the stairs, I don't know what else can be done to prevent him from climbing the stairs, honestly! You can have a wrought iron gate built that's higher than a baby gate, and that would have a locking mechanism on it as well. It would be too high for him to climb, so that could be a consideration, albeit expensive.

The other idea I have is to place a round black rug at the base of the staircase(s). Many times, a dementia sufferer will think it's a 'hole' and not get anywhere near it. They lose their depth perception and the rug looks like a hole. I have a doormat at my house that looks like a manhole cover.......not for dementia purposes, just because it's cute and I like it!

https://www.amazon.com/s?k=manhole+cover+mat&ref=nb_sb_noss_2

At first, you'd have to be careful he doesn't trip over it in case he's curious and wants a closer look. He probably won't though, so it may actually work.

Good luck!