I once had a dog that pooped wherever he wanted to, usually on the deck right outside the house. The way I solved the problem was this: scoop up the poop, take the dog and the doo to the place where you want the dog to go. Show him and tell him that this is where he should go, petting him and giving positive feedback. Clean the area where the dog went originally so that no scent is left over. If you do this each time, the dog will get the idea that it pleases you if he goes where you've shown him to go. It worked really well with my dog--he even was very specific about the exact spot he went after that. Took only a couple of times, and he had it!
Good luck!