Stacking is an essential skill that your dog must learn in order to look his best at conformation dog showing events. The dogs who are the best at it make it look easy and quite natural looking. So much in fact, that many people do not realize that it is a skill that usually has to be taught. Most dogs do not naturally stand in the ideal stacking position while at rest. There is an art and a science to getting the movement just right.
While you are teaching your dog how to stack, be aware that the rest of your dog will tend to follow where his head goes. If his head is crooked, drooping, or too tense, then the rest of him will tend to be out of place. If your dog is having trouble understanding something and moving completely into the correct position, then you can break the steps down even further and reward him for any effort toward the correct movement.