I have a Great Pyrenees livestock guard dog. I have an under ground electronic fence that I trained him on when a puppy. He goes on duty from dawn to dusk every day, rain or shine, and never leaves the property. I have observed him run a Coyote to the property boundary and my dog never crossed it. The Coyote, however, crossed it at a high rate of speed. Now, bad actors never venture in to his patrol area.
Sorry to hear this Great Pyrenees was left to run on his own. When untrained they are roamers.