Real cops don't do it for the money
The sheep do not want the dog around.
He looks too much like the wolf. He reminds them that danger lurks out there, just beyond the fence.
The wolf hates the dog. He knows that it is the dog that stands between himand his prey. It is because of the dog that he is lean. The dog is the reason the wolf is forced to lurk in the darkness.
The dog knows these facts. Undeterred, he stands watch, ever ready to do battle against the wolf. Despite the fact that he is an unwelcomed guest in their midst, the dog is ready at a moments notice to give his life to defend the flock.
it is simply who he is:
the police.
https://www.youtube.com/watch?v=2zyhOW-8Zcc