There are many reasons a person would want to train his dog to eliminate in one area. Service dogs are trained to do it because if the person who has the service dog wants to go on a cruise, for example, and needs her service dog to eliminate on a patch of grass on the ship, or on puppy pee pee pads, this training would come in handy. There are several ways to train your dog to eliminate in one spot.
Attach a command to the act of elimination. When your dog is still a puppy, begin training him to eliminate on command. To do this, bring your dog to the area where you want him to eliminate, be it a spot in the yard, a doggy litter box, puppy pee pee pads or simply a newspaper spread out. Give a command such as "go potty" or "hurry." As soon as your dog completes the act, praise him exuberantly and give him a treat. Do this every time he must go out and he will get it in no time.
Rope or fence off an area in the yard where you want your dog to eliminate. Bring your dog to the area where you would like him to eliminate on a leash. Put him inside the area and take the leash off. You can use an x-pen (exercise pen) which works well for this application since it can be arranged in any shape or size. Leave him in the area within the exercise pen until he eliminates. As soon as he has completed the act, praise him and allow him to leave the area. He will catch on quickly that in order to re-join you in your home, he must eliminate in the area in which you have placed him.
Set up an area within your home if you are training your dog to eliminate inside. This is a good idea for people who are disabled and cannot walk their dog, or those who live in areas where the weather makes it difficult to bring the dog outside, such as winter storms or hurricanes. When you see your dog circling an area, bring him to the area you have set up with newspapers, pee pee pads or a dog litter box, and wait for him to eliminate. Once he has done so, praise him and give him a treat for completing the act.