Most manufacturers provide a pull weight recommendation which offers you more information on how durable the leash is. Some can withstand weights of up to 550 lbs, making them suitable for the toughest of dogs who try to pull away. The leash should also give you an indication of what size dog it is designed for. If you are concerned about your dog pulling too hard on it, you should choose one which is made of a tough material like leather or durable nylon.