.2.2.1.1 Shooting Boxes and Fault Lines should be constructed of
wooden boards or other suitable material, must be fixed firmly
in place, and provide both physical and visual references to
competitors. For hard ground surfaces clear of debris, 0.75
inch material is the minimum allowable size. On other range
surfaces, such as covered with turf, sand, gravel, wood chips or
similar, thicker material which rises at least 1.5 inches above
the surface is recommended.