My 13 month old shitzu all of a sudden started peeing anywhere except the puppy pads.
He's always been very good about using the pads. He has not been neutered yet. Would that have something to do with it?
Hi I would guess that your pup may be 'scent marking' rather than actually peeing. Un-neutered males will do this frequently, and it's got nothing to do with housebreaking or a need to urinate. It's a territorial behavior.
You'll need to correct him verbally if you see him lift his leg, then redirect his attention. While he's learning, you can use 'belly bands' (sort of like doggie diapers) to protect your carpet and furnishings. I'd also recommend having him neutered to minimize this. Although it's more difficult in a dog who has already started to do this than in a pup who hasn't got to that territorial maturity yet.
If you don't think he's marking, but is actually having a problem controlling his urination, then I'd suggest having your vet take a look at him. It could be that he has a UTI (urinary tract infection) that is causing this behavior.
Sometimes this sort of thing can also be a sort of 'acting out' and a reaction to stress or change. If you've moved house, added a new dog (or other pet), had a new baby, gone back to work, or made any significant changes in your life recently, this could be your dogs way of expressing his anxiety. In this situation, simple and consistent loving corrections should overcome his issues.
I hope this helps some, best of luck with your dog.