
Light - A regular system of lighting with torches, fire, or death is needed to prevent hostile mobs from spawning within the protected area.Coverage - All defenses need to completely defend the protected area or defense, so that mobs entering from any side or angle and of any type will not break through.

As such, integral to all Minecraft defense systems:

Some of the best defense measures are those that prevent hostile mobs from spawning entirely or at least prevent hostile mobs from ever getting close to the protected area or defense mechanism.
