Dogs have it great, if they get proper dog training. They have the entire world as their dog bathroom. Dogs can urinate anywhere they please.
Male dogs really appreciate this convenience. So, how can you train your dog to go in a specific spot in your yard? The first instinct of a dog is usually to go where the scent is right. There are certain odors that your dog will be attracted to when searching for a place to urinate. Common areas of attraction are of course, right on top of where another dog has pottyed and anything that tends to be upright.
The first step you need to take if you decide to have your dog only go in one place, is to put your dog on a leash, take him outside and direct him to the area where you want him to use the bathroom. The instant he/she goes potty in that area you praise, then give a high value food treat. The message is that they did a great job of going potty right where you wanted them to go. You do this everytime your dog goes out to potty. This takes time and patience but it works, eventually.
A shortcut to this is to purchase a spray or drops that attract your dog to a certain area where you want it to go. Have your dog inside the house. Place a few drops or spray where ever it is you want to dog to urinate, then take your dog to that area. Give him the command you use consistently to tell him to potty, let him sniff the area and get familiar with it. When he successfully potties be sure to give praise and a high value food treat. There are also vertical posts you can purchase at pet stores, that are coated with a pheromone spray that you place in your yard where you want your dog to potty.
The dog is attracted to the scent, marks the territory by urinating on it, you praise and treat. As with all training, consistency and repetition win the game. Be as comfortable with the trainer of your dog as you are the teacher of your children. And remember, Opportunity Barks!