SportDOG In-Ground Fence System, SDF-100 In-ground fence system for dog containment and training 4 adjustable electric correction levels plus beep- and vibrate-only modes 1,000 feet of wire and 100 flags included; expand the area with Wire and Flag Accessory Kit (SDF-WF) Limitlessly expandable for more dogs with purchase of additional collar-receivers Anti-linger feature keeps dog from pacing boundary's edge