My 90 year old father is pooping himself. What do I do?

Yes check the foods he eats. I cut out coffee and apple juice with Mom. Did a number on her. I caught a new aide offering her coffee at dinner. I told her Mom is not to have coffee. I got a weird look. I then told her "you give her coffee, you pay the price". She had Gerd too so Dr. had said to cut out.

See if its a certain time of the day he goes, like after meals. Then get him to the bathroom at that time. Or maybe its just his brain can no longer send signals telling him he needs to go.

Think twice about bringing him into your home. The only couple I know who did it successfully was where the husband did anything intimate for his FIL. Me personally, would not take care of a man unless my husband.

Make sure he's wearing Depends or something on that order. It's not going to get better, so if you're responsible for his care, it may be time to place him in the appropriate facility, where he will have folks that are trained to change and clean him up.
For most folks poop incontinence will be the straw that breaks the camels back.

His medications could be causing the issue, too, so follow up with his doctor.

There's an anxiety medication that the dad of a friend takes (he, too, has Alzheimer's), and it absolutely liquified his intestines. If your dad is on one of those meds, alert the doctor.

I think that you will need to consider placement for your father if you feel as though you cannot handle this 24/7 intensive care. I would certainly not be able to do it, and I spent my career as a nurse. Your Father may have many more needs other than incontinence. Do consider whether or not you can continue in this care. It's crucial we know our own limitations.

Angieszoo, in short, what you do is contain and clean. Containment by using absorbant, disposable underwear (Attends, Depends, etc.) and clean by going into the bathroom with your dad and cleaning him while he's on the toilet using disposable wet wipes (and whatever else works, but don't flush wet wipes) and helping him shower whenever necessary for complete cleaning. Repeat as required -- might be several times every day. Discuss this with your hubby and decide if you're both in agreement to have a trial period of your father living with you. I suggest not making long-term plans just yet for him living with you. A trial period will allow you to better see if there's any real chance of a longer-term commitment being a good idea. You could also get your father an appointment with a gastrointestinal specialist and go to that appointment with him, but know that it's fairly common for those specialists to not have any good solutions for patients with Alzheimer's dementia, other than contain and clean. Kudos to you and hubby for wanting to help your father. Best wishes for all of you during this hard time.

This info from your profile will be helpful in answering your question:

"I am caring for my father who is 90 years old, living at home with age-related decline, alzheimer's / dementia, cancer, incontinence, and mobility problems."

You also state:

"Looks like father will be moving in with hubby and me."

Many on this site will urge you to consider alternative care rather than having him move in with you. It will be life-altering and exhausting for you and your husband in ways you cannot currently imagine, not to mention the emotional and even financial strain it will put on your relationship with your husband (the innocent bystander in all of it).

As for your father's bowel incontinence, I'm assuming you are already using adult disposable undies, like Depends? Is he removing them? Or is he having diarrhea? Can you please be more specific about the exact nature of the problem?