Ummm No ! I would not tolerate this at all. I’d have a sit down talk about this and be very clear whether it’s “his” bathroom or not , now the dogs are marking ??? NOPE !

Personally I’d leave a bottle of cleaner and paper towels on the back of the commode and tell him to clean it daily, and better yet SIT down.

I’d be queen B over this, so nasty , I’m sorry you are dealing with it