From Pathfinder Battlecry!, which isn't enabled.

Perfect Protection

FEAT 18

Your armor protects you from the deadliest hits. Each time you're critically hit while wearing the medium or heavy armor, attempt a DC 14 flat check. On a success, it becomes a normal hit.

Special If your armor has a Fortification rune, you roll only one flat check, but the DC is 12 (or 10 if it's a Greater Fortification rune).

Pathfinder Battlecry!ORC