Jason Blue arrived home from work at approximately 5:45 pm. As he approached the front door, he heard his pet Rottweiler, Zeus, barking and growling. As Mr. Blue entered the home, he realized that there was an unarmed man pinned to the ground by Zeus. Mr. Blue quickly retrieved his 40-caliber gun and shot the intruder in the head, rendering him dead.

What is Mr. Blues's best defense available to justify his actions?