It may border a street, woods, a residential area, an industrial park, a shopping center, a body of water, or an open field. The school or its neighbors may have erected fences or gates to prevent visual or physical access. The school may have a complete or partial fence with or without gates, but however substantial or inadequate, it usually stands as the first perimeter of the school property. If the school has a fence, its purpose may be to serve as a barrier to intruders or to prevent students from leaving the campus. Schools with complete fences on the perimeter can achieve a higher level of security than those without them.
Fences are also more important if the second and third perimeters of the school are weak.
The school s second perimeter consists of the facility external doors. Newer schools, which generally have all of the school s spaces under one or connecting roofs, can sometimes lock all external doors except the front entrance as a means of controlling access. Schools with multiple buildings or portable buildings usually have more difficulty locking these doors because students must move through them. If a complete fence is present, locking external doors during the day is not as critical as it is if the campus is not fenced. The external doors may have to remain unlocked, but if so, a procedure should exist so that they can be locked quickly if a threat is identified.