A staple gun and a method of using the same. A stapling mechanism in the housing is activated to deliver a staple through an aperture in a housing wall and drive the staple into a surface around a stack of one or more electric cables. The gun includes a reciprocating cable guide for centering the gun on the stack of cables and closing a safety switch to permit the gun's trigger to be activated. A spacer extending outwardly from the housing wall rests on the upper surface of the cable stack. The spacer and a bumper that engages a hammer of the stapling mechanism provide for automatic depth adjustment when driving the staple into the surface. A reciprocating cable guard extending outwardly from the housing wall is positioned between the stack of cables and the staple to aid in preventing the staple from piercing the cable.