A barrier is an obstacle that defines the limits to an area and prevents penetration by persons, animals, or vehicles. It can be either natural or artificial, and both types can be incorporated into a security operation.
A basic security concept is to surround your target with multiple barriers, a concept known as defense in depth. This allows for a mixture of deterrent and delay barriers. Perimeter barriers should properly warn an intruder to keep out, either with explicit wording or intuitive design, and thus defeat an intrusion without actually being tested. The explicit display of present security and property demarcation eliminates any chance of accidental intrusion.
Barriers that are meant to function after the perimeter is breached operate differently under the assumption that any intruder past that point has willingly and purposefully ignored deterrent measures. At this point, the purpose switched to delaying the intruder. Any physical barrier can be surpassed with enough effort and time, therefore the design logic should not be to prevent the possibility of the barrier being breached, but to make it require so much effort that it is not worth it, or so much time that the intrusion cannot be completed.
Exploring What Creates A Protected World