Cujo extension can be used in a variety of ways. Used with the Cujo or Mutley leash it adds more leash, can be used as a check collar or can be used as a restraint around a pole. With 2 Cujo extensions you can now walk 2 dogs on one leash and because it has 3 swivel points your dogs will never get tangled up! With 2 different lengths available you can walk large dogs with small dogs. Also thoughout the entire length of the extension is reflective strands for night safety.