Methods and systems are disclosed for drilling counter sink fastener holes in composite materials with conductive foil lightning strike protection systems. Initially a non-destructive depth detector is scanned over a prospective fastener hole location. Then the depth of a conductive foil below a surface is detected. When the detected depth is less than a predetermined depth, a signal that indicates that a countersink fastener hole may be drilled is output. When the detected depth is greater than a predetermined depth, a signal that indicates that a countersink fastener hole may not be drilled is output.