When building a run for your dog, the size and shape is important. First, your dog will get better exercise in a long, rectangular run than he will in a square one. The run itself should be at least four to five times as long as your dog, from the tip of his nose to the base of his tail, and twice as wide. If you're limited in space, don't be sparing with the length. Where you locate the run is important too. Your dog will need some shade in his run. An ideal spot is one that has a full day of shade, but even one that is well-shaded in the afternoon can suffice. Otherwise, at least part of the run should have some type of solid panel or plastic cover over it to provide shade.