In my own front yard here in Slat Lake City I would probably not shoot the idiot throwing rocks but in a war zone Where the first projectile is a rock the second could very possibly be an explosive device, in that case automatic weapon fire seems justified.
I'd use a non-lethal weapon.
If the @&& hole is throwing rocks at you he obviously wants to hurt you, if rocks don't do anything then he will move on to something that will, shoot the B|tch before he gets you, shoot him in the leg if you don't want him dead and the scar will remind him not to be a dumb@$$ and throw crap at a guy with a gun.
Also, if you see some guy holding up a convenience store with a gun are you gonna walk in and throw your shoe at him? Will he pull out a tazer to take care of you? I honestly don't think so.