A variable retaining wall system may include a block having a top, a bottom, and a hollow core area. A light probe, adapted to be mounted on the weapon proximate the optical pathway of a sighting beam of light generated by a laser sighting device, is provided for detecting the sighting beam and producing in response thereto an electrical detection signal. One or more channels on which to serve each segment are determined, and a rate at which to serve each segment is determined. This identifier may, for example, be a persistent state object or cookie. The shelf is coupled to the first and second end plates and includes a first and a second shelf pin.