4. Failure to teach according to the dog: There are huge body differences among different breeds of dogs, and the dog’s comfort will affect the effectivenss of training.owners should decide whether to choose a dog harness or a dog collar based on dog training of different sizes and personalities. For some small dogs or shortnosed breeds (such as French bulldogs, pugs, etc.),pet collar may increase the risk of breathing difficulties. For large dogs (such as German Shepherds, Golden Retrievers, etc.), if you choose an inappropriate dog harness and leash, it may irritate the dog and attack the dog owner.