Replace the Fence Transmitter for your SportDOG Brand® In-Ground Fence™ system or Contain+ Train™ system, or create a containment and training system with your existing SportDOG Brand Remote Transmitter by pairing this Fence Transmitter with the Wire & Flag Kit (SDF-WF) and the Contain + Train Collar Receiver (SDF-CTR). Features Expands up to 100 acres with purchase of additional Wire & Flag Kits (SDF-WF) Expands to any number of dogs for containment with purchase of additional Collar Receivers