The SportDog SD-425s Field Trainer offers all the features of the SD-425, but is an electronic dog collar specially designed for tougher, more stubborn dogs. The Sport Dog 425s is ideal for training in the yard, field, or for hunting with dogs that hunt closely to you but tend to be a little bit stubborn. This unit comes with a transmitter and receiver that are 100% waterproof and submersible up to 25 ft. It comes with 16 levels of continuous or momentary stimulation and can be expanded up to 3 dogs by simply adding SportDog Brand Add-A-Dog collars. It also features a tone or vibration that is available in multi-dog use.