Would you consider using a piddle pad? That might be the easiest and most effective way to train him. My boys are both pad and outdoor trained. If you do go the piddle pad route, you would always have to make it available. It wouldn't work if used only sometimes or part time.
If you still want to do 100% outdoors, keep in mind that little dogs need to go fairly often (although not every 15 minutes
).
You have a big training job because he was accustomed to having on a belly band.
If you have not already, institute a potty break schedule. Take him out immediately when he wakes up (from sleeping or napping), right after meals, maybe another 30 minutes later, every time he gets excited (doorbells, play sessions), and before bed. Also, in the early stages of training, you may want to treat him like a puppy and take him out every hour.
If you work and cannot supervise this much, I highly recommend the piddle pad plan.
When he potties in the right place, praise him profusely like he just performed the best trick ever. Give him a little treat (it can be a single piece of kibble). When he has an accident indoors, do not scold. Just clean it up with an enzyme cleaner to remove the scent and to prevent him from wanting to return to the spot.