The gorilla, the guy, and the balls

A guy walked out to get his mail in the morning. He turns around and there is a gorilla. So he runs back inside, opens the yellow pages, finds the only gorilla exterminator in town, and calls him. The exterminator arrives in a little truck towing a cage. The exterminator has a ladder, a gun, and a dog. 
  The guy says, "How are you going to get the gorilla off my roof?" 
  "I am going to put the ladder up against the side of the house, get up there, wrestle the gorilla, and toss him off the side of the house. When the gorilla hits the ground, the dog is trained to grab the gorilla by his balls and drag him into the cage."
  "What is the gun for then?"
  "If the gorilla throws me off the roof first, shoot the dog before I hit the ground!"