*** Any ideas about how I can effectively potty train him? ***
You mention that you take your dog to the same area when you take him out to 'toilet', I suppose thinking that he'll associate that spot as his bathroom(?). But I think you would be more successful if you took your dog out for long walks.
Your dog needs exercise anyway, and movement begets movement (if you know what I mean). Besides, walking is a very social activity for dogs. They walk in packs and when you walk with your dog, you become part of their pack. Some people like two half hour walks each day. Personally, I try to get one really long walk in every day (weather permitting), typically 3 miles or 90 minutes. Sometimes shorter, sometimes longer. (I got bored walking the same route. Now we go different places (local dog parks, woods, and such) and explore new routes. Mix it up a little.
The walk provides time for the two of you to bond. It's an opportunity for you to reinforce training, provide encouragement (and praise). And it allows your dog to eliminate (or toilet), naturally, without pressure.