The fox has always symbolized someone devious and duplicitous. Like George Clooney. On the contrary, the dog was very loyal and honest. The fox and the dog is a metaphor of the Satan and the God. And so, as early Christians believed, when the dog becomes lazy and the fox jumps over it, the Apocalypse will happen. That's why the dogs have always been trained in order to never become lazy and to chase foxes down.