but a belly band isn't going to teach him to go outside...you'll just be changing the belly band for the next 10-15 years.
Make sure you're cleaning up after him with an enzymatic cleaner (it should say it contains enzymes). He needs to be on leash all the time unless you are not home/are asleep in which case he can be crated. You can also crate when you are very busy doing something (like cooking dinner). The point of the leash isn't so the dog won't go, they could care less whether or not you are around, it's just going to the bathroom, there is nothing wrong with doing that around others in the mind of a dog. The leash is so you can notice behavior that signals the dog has to go (dog unable to settle, sniffing, pacing) and respond. Even if you think he looks like he has to go for a second, rush him out, you can never take him out too much. The leash also enables you to see the moment the dog begins to squat. Pick the dog up right away and take him out, even if he was in mid pee (assuming he doesn't continue peeing after you lift him).
Take him out as frequently as you can, every hour or two is good to start. Even if he holds it in the crate he still must build up a really strong habit of only going outside.
The dog either needs to be leashed or in the crate at all times. Reward with a treat and praise when the dog does his business outside.
This should work whether it's pottying or marking. On walks let him mark as much as he wants. If he's not neutered that might help if it's a marking issues. A vet visit might be in order to make sure it's not an infection or something making him want to pee so much.