Size
Of course, this aspect matters most. It is important that the collar will fit comfortably on your dog's neck. Do not make random guesses as to how long the collar should be.
Before going to the pet shop, try to measure your dog's neck by using tape measure or any string or tape that can be used as a guide. Then, try to make some allowances, say, 2 to 3 inches more. You can never be too sure about the actual length of the item; hence, it is best to make room for extras.
