High quality dog leashes have a good quality metal clip and they can be made of leather, nylon or even chain. The metal clip must securely fasten to a metal ring on the collar in order to maintain good control of the dog. The material of which the leash is made of is not of great importance as long as the leash does not show evidence of wear or fraying. Therefore, leashes should be periodically checked to ensure they are maintained in proper condition.