Get a crate and lock him in it, only let him out when you are taking him outside to pee. A dog doesn't want to pee in his bed, so he will wait until you go outside, he will have no other option if you keep him locked up. In a short time he will learn or rather train himself that outside is the place to go. Anyway, that has worked for every puppy I've ever had, it should work with an older dog too. Another thought is maybe he's just unsure of his environment, and when he adapts it will be all good again. Either way the crate should help.