This was a dog protecting his home not some random bite in the street or park. I'm always watching for dog's on properties that I del to. Some dogs just have a natural instinct to be protective. It's the owner's responsibility to know their dog, its tendencies, and control it.Its too late for that.
A dog that bites without provocation needs to be put down.
Next time it could be a little kid that gets his or her face torn off.