Is there anything I can do to stop my cat from peeing on random things in the House?

He is 1 of 3 cats. At one point he had a bladder problem that made it painful for him to pee however he is currently on medicine and special food to help with that. He is an outside/inside cat he spends most of the day outside yet he will still pee on this one spot of carpet in the house and anything we put over it. I don't want to have to give him away or worse but He is destroying the carpet and parts of the house. Please help!