The application is agriculture and other outdoor, multi-acre areas. So, InterSense products won't work. And ultrasonic sensors in general won't work. I'm actually working on developing a device using RF and multiple transponders positioned around the field. I've searched around the Internet for anything similar and haven't seen anything, so I think my approach is unique. But you never know, there may already be something out there. That's why I asked on this forum, to see if anyone might know of an existing device.
There are two types of animal tracking. One simply identifies the animal, as when a cow passes through gate, and it does that using RFID technology. That does not actually determine the position of the animal. The other type is when a transmitter is attached to the animal. This can include a GPS device, in which case the resolution is still limited to about ten feet, or without a GPS unit it requires directional antennas used by human trackers and that only gives very general direction and range information.
So, no, the animal tracking techniques would not work.