Perimeter defenses help prevent, detect, and correct unauthorized physical access. Buildings, like networks, should employ defense-in-depth. Any one defense may fail: so critical assets should be protected by multiple physical security controls, such as fences, doors, walls, locks, etc. The ideal perimeter defense is safe, prevents unauthorized ingress, and when applicable offers both authentication and accountability.
Fences may range from simple deterrents (such as 3-foot/1-meter tall fencing) to preventive devices, such as an 8-foot (2.4 meter) tall fence with barbed wire on top. Fences should be designed to steer ingress and egress to controlled points, such as exterior doors and gates.