I want to hang 3 guitar hangers up, and the wall behind the drywall is an outside concrete wall. Obviously I can't use drywall anchors here (that would mean HUGE holes in the concrete), so I am guessing some sort of concrete screw/anchor system. I can't really see the concrete but can feel it with a screw right behind the drywall, so anyone who knows this stuff better than I do know the correct way to secure these things?