When I first got my APBT puppy, I immediately taught her the command to "go potty". How I did that was, any time we went outside, I did nothing but give the command. We didn't play, she didn't hear me say anything else until the job was done. And now it doesn't matter where we are, she will potty on command.
Seems like your dog is playing games with you. Believe it or not, dogs are capable of doing it. Go out side with him every time, give him the potty command if you would like. If he doesn't go potty, then he goes inside and right into his crate or safe zone. Don't give him the opportunity to potty in the house. 15 mins after this, try it again. Its obvious that just leaving him outside isnt going to do the trick, but maybe you're not leaving him out long enough. The only hard part about leaving him out for extended periods of time is that you'll never really know when and if he does go potty, unless you're watching him like a hawk. Which is why I would suggest that you be there with him. Become a statue, be boring. Don't interact with him, don't pet him, don't even really look at him. Just repeat your command, "go potty". When he finally does, become extremely animated. Its good to go potty! His reward for going potty isn't a treat, its you.