Extra Dogtra Pathfinder Collar
Additional collars for the Dogtra Pathfinder GPS System, available here without GPS receiver.
The Pathfinder system allows you to track up to 21 dogs.
Only 1 GPS receiver is required per group of dogs, so you do not need 1 receiver per dog. If multiple people want to track the group from different locations (e.g. a hunting party), they will each need a GPS receiver.