MT902-A In Ground Fence, Wire Electric For 2 Dogs Fence with Rechargeable & Waterproof Collar Speed Detection: Your Dog Is Moving Faster, The Higher Level of Intensity Is Issued. Proportional Shock: The Closer Your Dog Gets to the Boundary, The More Intense Shock Will Be. Audible and Visual Wire Break Indicators Add an unlimited number of pets by purchasing an extra collar (search asin:B01FF1W966) for each pet. Update to Two Receive Extra Collars