Dog doesnt hold his pee when alone

My dog is 4 years old. Ive had him since he was 8 weeks. The past 4 or 5 months hes been peeing on the floor EVERY time I leave the house. Hes not super anxious but hes high energy. I exercise him plenty every day. If I'm home with him he can go like 5 or 6 hours without going outside and overnight is never a problem when I'm home. But if I leave for 3 hours and take him out right before I go? He pees. So its not that he CANT hold it. And he definitely knows its wrong. I come home and hes in the corner acting all sheepish. I pull him over to it and scold him and then take him outside to pee and if he does I praise him for going outside. I thought the problem might be a residual pee smell that hes just peeing over but I've moved in the past month and he immediately peed in the new place the first time I left him. Ive tried crating him and it doesn't work he just pees in it. The only thing I think might be related is that recently hes started marking. The first 3 years I had him he didn't mark once outside. His pee isn't dark and smelly but could it still be a UTI? If not why would he be peeing after such a short time alone?? I'm thinking of taking him to the vet. Sorry for the long post. Thanks