Describe defense in depth and provide a practical example in a facility.

• A. A single locked door that stops all threats
• B. Layered security measures across people, processes, and technology, such as fences, access control, cameras, patrols, and trained staff.
• C. Security by obscurity
• D. Only perimeter fencing

Answer: (B)

Defense in depth means building multiple overlapping layers of security that protect a facility across people, processes, and technology. The idea is not to rely on a single control but to have several barriers that work together, so if one layer is breached another still stands, buying time to detect and respond.

In a facility, you’d start with a strong exterior barrier like fencing, gates, lighting, and clear sightlines. Then add controlled entry points with badge access, turnstiles or mantraps, and procedures for screening visitors and packages. Inside, deploy cameras, intrusion sensors, and secure doors that are monitored, plus regular security patrols and trained staff who follow documented procedures for deliveries, access, and incident response. Ongoing training, background checks, and drills reinforce the human element, while redundancy—backup power for cameras and locks, separate systems for critical operations, and a clear incident-response plan—ensures continuity even if one layer fails. This layered approach makes it much harder for threats to succeed, because breaching one barrier doesn’t immediately defeat the overall protection.

A single locked door cannot stop determined threats, and relying on perimeter fencing alone leaves interior access and operations vulnerable. Security by obscurity is unreliable, as secrecy can fail and does not provide robust protection by itself.