Untraining a puppy pad trained 6 month puppy.

Hello – we got our pup, Frank, at 17 weeks. We hadn’t been told that he had NEVER been outside. Only ever used puppy pads. Now it’s been 8 weeks if diligent routine, bell on door training, crate training, every area rug has been removed… now he’s peeing in the couch. Sometimes he signals us by sniffing, pacing, occasionally he rings the bell! But sometimes, typically in the evening he’ll be playing or chewing something get up, walk somewhere and just pee! With no warning. I do try to interrupt him and bring him out but he typically just keeps peeing. Even if I pick him up. This will often be within 15 minutes of him going out. He’s a 6 month, 10lb, poochon. HELP!!! Please…. Feeling defeated.