This PetSafe® Stubborn Dog In-Ground Fence extra receiver collar can be used to add another dog to your PetSafe® In-Ground Fence system or as a replacement collar (not compatible with the UltraSmart® and YardMax® systems). The collar features 4 levels of static correction at a higher intensity especially for stubborn or hard-to-train dogs. Waterproof Receiver Collar Add Unlimited Pets to Your System Adjustable Collar | PetSafe ® Stubborn Dog Receiver Collar