So.........reading between the line, it sounds like you may be saying your loved one who has Dementia/Alzheimer's stands up during a meal and pulls his/her pants down? Is that it? There is no rationale to this brain disease; nothing makes sense. You can purchase an Alzheimer's jumpsuit online (Amazon.com) that zips up in back and prevents a person from undressing himself or removing an adult incontinence brief while awake or during sleep. These garments are particularly useful for those who prefer to be naked!
Gotta learn to laugh at the truly absurd things that they do.
-Abraham Lincoln
https://www.amazon.com/Talit-Inc-Womens-Alzheimers-Clothing/dp/B07KPPLZM6/ref=sr_1_1?crid=1Y74RA6682XK7&dchild=1&keywords=alzheimers+jumpsuit+with+back+zipper+womens&qid=1578967522&sprefix=alzheimers+jumpsui%2Caps%2C176&sr=8-1
Best of luck!