 Some of the key concepts underpinning dynamic defence, are "deliberate erratic actions" and "attack zones"- the surfaces or spaces vulnerable to attack.In military tactics, the deliberate use of "erratic action", forces an opponent, subjected to hit-and-run attacks without warning, to remain on constant alert; and which deliberately wears them down.Examples of erratic tactics used in terrorism are where attacks are opportunistic, and targets selected have only a generic relationships with the supposed political aims of the terrorists involved.