Got Your Back (Combat, Teamwork)Source Melee Tactics Toolbox pg. 10 (Amazon)
You protect an ally from attacks he doesn’t see coming.
Prerequisites: Int 13, Combat Expertise.
Benefit: If you successfully use the aid another action to give an ally who also has this feat a +2 bonus to AC against an opponent’s next attack, the ally is also not considered flanked or flat-footed against that opponent until the beginning of your next turn.
Normal: You can use aid another to grant an ally a +2 bonus to AC against the next attack from an adjacent foe.Source Armor Master's Handbook pg. 20 (Amazon)
If you spend 3 stamina points when you use this feat, your ally benefits from the AC bonus until the beginning of your next turn. (Melee Tactics Toolbox 10)