How to tunnel proof your prison (exploit)

[MFWIC]

No dogs required. Build a second fence at least 5 squares away from your main prison wall. Design this fence with no doors or gates, and set it up so that its only openings come out next to an armed guard or guard tower. Due to game mechanics, tunnelers will stop digging once they're outside the main wall, but still inside the confines of the secondary fence and simply be funneled into a capture zone. The AI will not flag the fenced area as a security zone because there are no doors.