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Talk to a certified dog training professional. Purchase a collar.

Article:
A prong collar is not simply another piece of walking equipment like a harness or a gentle leader. It is a training device. A prong collar should not be used without consulting a professional dog trainer.  A certified dog trainer will likely have experience using  a prong collar or choke chain to discipline a dog. If used incorrectly, prong collars can be ineffective or even painful.  A prong collar is used as part of a longterm training process that teaches your dog why pulling is not appropriate. It should not be used for walks that occur outside of training time. Casually using the collar for walks does not teach your dog pulling is inappropriate. It only teaches him pulling while wearing the prong collar is inappropriate. Talk to a trainer about how and when to best use the collar. Many people are wary of prong collars due to the potential for pain. However, purchasing the right kind of prong collar lessens the likelihood your dog will experience pain while wearing it.  Quality prong collars are designed to gently pinch the loose skin around the dog's neck, providing negative reinforcement in the event of pulling and misbehaving. A good collar will never puncture your dog's skin. The right size is important. Collars are divided by weight distinction, so know how much your dog weighs before selecting a collar. If you buy a collar labeled "For 100-120 pounds" for a 75 pound dog, this is far more likely to cause your dog pain and discomfort than a properly sized collar. Buy a collar from a certified trainer or a certified trainer's website. Prong collars sold at chain stores like Petco are often not as well made and the prongs have sharp rather than rounded edges. This results in puncturing rather than pinching your dog's skin, which can lead to aggression during training sessions. Never buy a prong collar with rubber-tipped prongs. Many people think such an investment is more ethical but rubber can rub against your dog's hair, causing pain. Metal, on the other hand, moves smoothly over a dog's coat.