The retractable dog leash is one of the most dangerous leashes for the dogs because they allow them to go as far as they want. Retractable leashes are usually made of nylon and the retractable device is made of plastic or a stronger composite. Although these leashes can be convenient for both the dog and the owner as it allows some control, they make it difficult to keep a dog under control which can result in persons or other dogs being attacked. Aggressive dogs should not be walked with such a leash, and puppies should be kept closely to ensure their protection from various dangers such as cars. Dogs with a tendency to bolt without warning should be walked with caution, as a retractable lead can allow the dog to accelerate to significant speed before being stopped suddenly presenting the possibility of injury to both dog and owner.