Trying to keep Mom out of my bathroom is proving difficult.

I guess u have the Master bedroom? So put a lock on your door and put a doggie door in for your dog. Or, buy a gate, they now have where they can be made permanent. Place it high enough for the dog to get under and Mom can't climb over it. I am assuming here dog is small since he goes under the bed. Maybe one of those temporary screens you see in the catalogs. It may stop her. I was going to say get a half door but u still have the dog.

The reason for the black rug is they think its a hole. No depth perception. No way to keep Mom in her section of the house? Like a gate somewhere. A door. Maybe hang a drape at your door. She may think its a wall. Make it the color of your walls. Like I said, they lose depth perception. Can you tell I am just brain storming here.

Put a lock on your bedroom door and let that be the end of it.
That is your space and mother is not allowed in there.
Keep the door locked.

Forgive me an observation- you seem a touch apologetic for attempting to reserve
a space in your own house for yourself and your pup.

You are doing more than many would to maintain the comfort of an elderly house mate now. Secure your potty with any of the suggestions you’ve received, and enjoy it!

Thanks for the creative ideas and support. I have a scared dog that hides out under my bed and have to leave the door open so he has access. I am going to try the black rug idea and last night hung a colorful scarf across the door frame on cup hooks to provide a visual barrier (dogs and I can go under it). Fingers crossed.

Amazon has tons of baby proofing things to put over door knobs.

Also, lots that fit over/under door handles that go up and down.

Which kind do you have? I can post the ones that have worked with my two year old grandson.

Can you try some kind of baby gate to put across your bedroom and bathroom door ways? If she has advanced dementia, hopefully she won't be able to figure them out. I don't blame you for wanting use of your bathroom all to yourself. Good luck in trying to get this issue figured out.

Put a small screen latch up at the top of your door. This will not be easily detected but will keep the door latched. Then you will only need reach up and unhook it when you want access.
Some folks with certain types of dementia will not cross a black rug or floor mat. You could place that in front of the door to see if it deters her.