My suggestion to you would be to keep him tethered to you at all times and do not allow him to have free roam of your house. Keep the belly band on him and take him out for potty only. You the tethering like you would with crate training a puppy but instead of going into a crate he needs to stay at your side. When you go out for potty, say the command and when he goes praise, treat and immediately back inside. Do not let him wander. Once you are sure that he does not need to potty he can have sort periods of freedom a little at a time. He is only going to potty in the house if YOU ALLOW him the opportunity to sneak off. Also buy more bellyband and they need to be if fashion statement for the long haul. Here is a link the Yorkie Haven Boutique:
Belly Bands*::*Yorkie Haven Rescue Boutique
If you make a purchase from the boutique all money goes directly to the Haven rescue pups

If it says that something is out of stock just email and inquire. Orders are filled quickly and we LOVE custom orders too
If you take a look in the Training forum there is a STICKY at the top of the page. It give all kind of great advice for puppymill rescues that apply to any dog that needs a little extra help.
http://www.yorkietalk.com/forums/tra...nt-advice.html
If you have any questions please just ask and I will try to help you as best as I can. Wishing you lots of luck. Be consistent and things will get better.