How to train your dog to eat food only from you..

[Sook]

Wide spred problem around the world i imgaine, peoples lovely family pets being nicked for scruplous reasons... Does/has anyone trained there dogs to be specific in what it eats and who its from.? If ya have, how'd u go about teaching him/her.?

Also, my boy has become rather "aggressive" when we are out in the car... If we pull into a gas-station, and anyone walks near the car, he raises hair and barks and snarls... Yet if we walk to the same gas-station and i stand outside waiting with him, hes all friendly and happy, not sure if hes posessive about his car or what.? Any ideas ?