Retaining Wall Stone - Interlocking retaining wall systems are used primarily in applications where the structural requirements call for a wall in excess of 4" in height. P&W Stone represents NicoLock Retaining Wall Systems with offerings for all applications, both residential and commercial. NOTE that walls in excess of 4' must be certified by a qualified Professional Engineer. P&W Stone, in conjunction with NicoLock, will provide design consultation.