Dominant dog collars are specifically designed for use on handler aggressive or dog aggressive dogs. These collars are excellent for lowering the drive and taking the fight out of a dog. DO NOT jerk this collar to deliver a correction. The proper way to use the collar is to SLOWLY lift straight up on the collar, until the dog ceases the behavior and settles.IMPORTANT - How to Measure for a Dominant Dog Collar: The dominant dog collars come in 1 inch increments. Use a string or cloth tape to measure around the dogs neck. Measure just under the jaw and around the head right behind the ears. The string or cloth tape must be tight to get a proper measurement. There should be no space between the dogs neck and the tape measure or string. Order a collar that is the same length as that measurement. If the measurement falls between two sizes, then round down to the next smaller size. For example, if the measurement is 18 1/2 inches, order an 18 inch dominant dog collar.If you were to lie the collar out flat with the floating ring all the way at one end, a 19 inch collar will measure approx 19 inches from floating ring to the top inside of clip. *See additional image.If you add inches to the measurement for slack, the collar will be too big and will not be as effective for training. A properly fit collar will remain in place and not slide down the dog's neck.Note: The dominant dog collar is not intended to give a sharp correction, it is intended to lower the dog's drive level.