Housetraining a dog is largely about reinforcing elimination in a location that’s desirable to you, and denying your dog opportunities to practice elimination in undesirable locations. Your dog doesn’t care, one way or the other about these areas you wish to protect from urine soiling
Just as you wouldn’t allow a naked newborn with a full bladder to sit on expensive furnishings without protecting them, you can control your dog’s access to areas you wish to protect from his urine. If you believe that your dog is somehow stressed or otherwise triggered to urinate in the presence of other dogs, consider managing that in a way that prevents the problem - no other dog contact until your dog is empty? Lead him to approved areas (on a leash) and stay with him, to effectively reinforce urination where you’d like it to be.
There are excellent clicker training resources available online. clickertraining.com is one. Karen Pryor and others have written scads of books about the process, but it is simply a clear means to communicate to your dog what he has to do to earn something (treat) he wants.