I would first make sure he doesn't have a medical issue like a UTI. Then start taking him out more often, treat him like a puppy. Every half hour or hour. Crated/penned or teathered to you if you can not keep a close eye on him. Only after he does him business outside do you give him some freedom. Also is he neutered? Could he be marking? Make sure to use an enzyme based cleaner to clean up his accidents and clean them up well or he will just keep going back to those spots. At night and when you are out you could put him in a pen, instead of a crate. That way if he does pee he doesn't have to sit in it. Remember to treat and praise like crazy when he does go outside. I still randomly treat Freyja when she goes outside, and she is over a year old. I just want to keep reinforcing it.