Perimeter fence
Demarcation of a perimeter, when the protection of assets, personnel or buildings is required, is normally effected by the building of a perimeter fence system. The level of protection offered varies according to the threat level to the perimeter. Different types of perimeter fencing include: Vertical bar fencing has been the most popular form of perimeter security fence since the 1980s. Since the 2000s, welded wire mesh and acoustic barriers have also become popular types of perimeter fence around the world. Vertical bar, acoustic barriers and welded mesh are used in commercial projects and landmarks, in schools, and  in airports and transport hubs. In high-security applications, sensors may be attached to the fence that generate alarms when they detect someone cutting, climbing, or lifting the fence fabric. Domestic and residential projects have since the 1980s featured timber fencing as the perimeter to houses and gardens. Ornamental metal railings have also been employed. In the United Kingdom, perimeter fencing is banned at any sporting stadium after the death of 97 people at Hillsborough Stadium.