Greater Ironclad Reactions (Armor Mastery, Combat)Source Armor Master's Handbook pg. 16
You are able to quickly react to attacks.
Prerequisites: Combat Reflexes, Ironclad Reactions, base attack bonus +11 or fighter level 8th, armor trainingclass feature, proficiency with medium armor.
Benefit: You can use Ironclad Reactions more than once per round, but not more than once for each act you take that provokes an attack of opportunity. Each 5-foot step you take still counts as expending one use of an attack of opportunity.Source Armor Master's Handbook pg. 20 (Amazon)
You can spend 5 stamina points to use this feat without it counting against your maximum number of attacks of opportunity for that round. (See page 16.)