Here's a followup to Conversing With Cat, the post about the cat with litterbox aversion that peed in the bowl of dry cat food.
I added a fifth litterbox to our household. I put it on the main level in the master bedroom. The other four boxes are in the lower level.
We have to keep the bedroom door closed now. Otherwise our huge dominant cat tries to pee in it and often misses. I don't mind if he misses the box in the laundry room. The floor is concrete and it's out of the way enough that we can cover the pee with extra cat litter. But this new box is right next to the bed, in front of the nightstand. So the Pee-meister sits outside the door and meows until someone opens it for him. Or sometimes I'll carry him into the room if I sense that he needs to go.
It's a solution in that he no longer pees where he shouldn't. But he's still wary of the other cats. And they still like to stalk him when he walks the long hallway after using the new litterbox. And he needs human intervention when he needs to go.
The ultimate solution is for him to get over his aversion to the litterboxes in the lower level. Not sure how to do that, except perhaps by moving the new (and presumably much cleaner) box downstairs and putting one of the old boxes in the bedroom. If he's associated the smell of the old box to his overall aversion, then he might avoid the box in the bedroom and seek out the new box in the lower level.
I'll keep you posted.