Defense in depth is the proposition that multiple layers of security are better than a single protection mechanism. The layers may be technological, procedural, or policy.
The opening sequence of "Raiders of the Lost Ark" shows a physical manifestation of "defense in depth". In it, Indiana Jones must defeat multiple disparate mechanisms (poison darts, open pits, rolling boulders, closing stone doors, pressure-sensitive floor tiles, spikes, etc.) in order to abscond with the idol.
