I have a real nice Testament Cd that would make them surrender. Listening to "Return to the Apocalyptic City" a few times would curl their toes. COC and Cannibal Corpse would do real well too. My favorite concert was 1988 Halloween night, Overkill, Motorhead, and Slayer.
They should get Motorhead to do a live show!!!(Lemmy is God)
All good choices. I'd throw in a bit of Man is the Bastard just for the pure creep-out factor.
I also highly recommend a relatively new band (newer than what were talking about anyways). Check out some stoner kings by the name of Electric Wizard if you ever get the chance.