Well, it is a gray area.
Where I am, legally, if a dog (Dog A) is on its own property, and another animal (Dog B) comes on the property, and Dog A either kills or injures Dog B, Dog A could be declared a dangerous dog, and there would be repercussions. Same goes for if Dog A is in its yard, and a human, authorized to be in the yard, or not, comes onto the property and is harmed.
Laws vary drastically from city to city, county to county, and state to state.
You should call your local animal control (often affiliated with the town animal shelter, or police department) for clarification on the laws in your area. They should have a copy of the code.
He who can no longer pause to wonder and stand rapt in awe is as good as dead; his eyes are closed. ~Albert Einstein