If I am out of hand grenades, I go for the Rem 870.
Grenades? Claymores!!!! Motion sensors. Can't have a guard panther then, though. Nor a guard gerbil, either, for that matter! Then it doesn't really matter how many come in with a layered defense of motion sensored claymores. Shoot, you could finish them up with a coup de grace from a squirt gun then.