Sportdog fieldtrainer x-series 425s for large dogs FEATURES:-Designed for high-drive, more stubborn dogs-Designed for ease-of-use & no look operation-Added more levels of static stimulation Other Features: 500 yard range, 21 instantly selectable static stimulation levels, low/medium stim ranges , tone & vibration options, rechargeable l-ion batteries expands to 3 dogs with add-a- collar system, waterproof, intuitive, no look operation lets you stay focused on your dog, for large/stubborn dogs