Have you tried some of the "No Dog" sprays sold at the pet stores? You spray it on the area that your dog is attracted to, and it's supposed to discourage them. Also, I would try some of the cleaning products found in the pet store that are specifically made to remove urine scent. It may smell clean to a human, but a dog can still smell the urine scent in the area and thinks he is supposed to go there.
Otherwise, I have had a couple of dogs that took quite a while to catch on to house training. They did eventually 'get it', and after that they were the cleanest dogs we owned. Good luck with your pup!
Every Christmas should begin with the sound of bells....