Structures designed to protect the areas around a slope from falling rocks include mesh or cable  nets, barriers and fences, and catchment areas (ditches at the toe of a slope, designed to prevent  rockfall from reaching the highway).  These devices allow rocks to fall but prevent them from 

causing any damage to a structure or the public. The protection can stop a rock, control its  trajectory, reduce its energy, and/or provide a catchment. In many cases, a catchment is used in  conjunction with an inclined deceleration zone.