I also imagine you could run some kind of flocking algorithm on the GPS units (pun not intended), where if the sheep herd suddenly scattered you'd know somethin

I also imagine you could run some kind of flocking algorithm on the GPS units (pun not intended), where if the sheep herd suddenly scattered you'd know something was up and how herd scattering occurs. Modern herd sheep are pretty stupid animals and scare easily, but with a big enough herd it takes quite a while to get them moving.