How do you train your dog to poop in one spot outside in the backyard and only that spot?

Dogs like to sniff and mark their territory and most dogs are extremely clean and prefer a clean area to do their business on. If you want to contain it use a doggy run (I have one) and the rest of the backyard is used so they can play. When it comes time to mow the grass I only have to clean up the doggy run.