Ключевые слова: abstract, background, barrier, border, bound, boundary, cell, chain, clip, close, construction, control, day, defense, dividing, fence, forbidden, frame, geometric, gray, grey, grid, guard, holding, industrial, iron, material, mesh, metal, net, no people, outdoor, prevention, private, property, protection, safety, security, separate, shape, shielding, simplicity, sky, steel, strong, structure, system, wall, wire,