Prong collars imitate a dog's bite, and when your dog pulls too hard on the leash, such kinds of collars tighten a bit and "bite" the dog on the neck. Such effect helps the dog to understand that he is doing something wrong.
Chrome Plated Dog Pinch Collar for Obedience Training
In fact, prong collars can be safe and very effective if used properly. Please note that this Collar should be worn high on the dog's neck. So choose this Dog Pinch Collar, it is a perfect variant for training dogs who have problems with obedience and behavior.
Reliable Prongs on Chrome Plated Dog Pinch Collar