First of all: if he can’t be trusted to hold his waste, he should NOT have free rein of the house.
I posted the following as a comment to another adult dog that isn’t housebroken:
do you have a crate? keep him leashed to you when you’re home so he can’t sneak off, and crated when you can’t supervise. take him out every 45 minutes-hour, and stay out there with him. when he DOES go, throw a party. when he doesn’t, pop him in the crate for 10 minutes or so, then back outside. rinse, repeat until he goes.
this WILL work, but you need to be diligent.
I would take ur dog to ur vet and make sure.