I say start at the beginning, with basic potty training (limit his free area again) and a GOOD potty treat! I use Peanut Butter chips from the baking isle. They are Yummy Rewards for good potty only...
Have you looked into the potty pads with the fake grass? Or are you strictly trying outside potty only???
DoggiePotty Indoor dog bathroom. Doggie potty a training solution.