Even if it's fitted correctly, a prong collar has the possibility of irritation by digging into your dog's neck and causing harm like red marks. This can be solved by investing in some rubber tips that fit onto each individual piece of metal that meets your dog's skin. By creating a barrier this way, you can make training a more comfortable experience for your dog. If the prong collar is causing visible pain to your dog, it might not be the proper tool for you or you may not be using it correctly.