Once upon a time, a harness was the last thing you wanted to use for a dog who pulled, because they were designed to make pulling comfortable. By distributing pressure evenly across the chest they removed pressure from the throat, where damage could be done to a dog's trachea sometimes even to the point of tracheal collapse. Harnesses are better for the dog from a health perspective, but from a training viewpoint, a standard harness actually encourages pulling. There's a reason sled dogs wear harnesses! Head halters were introduced in the late 1990s as a gentle control tool. While they did, indeed, work well to control a dog's head (and where the head goes, the body follows), some trainers noticed that a significant number of dogs found head halters to be fairly aversive, requiring, in many cases, extensive conditioning to convince the dog to accept them.