You appear to raise your shield to block your foes' attacks even before the creatures swing.

Daily   ✦     Martial, Stance
Minor Action      Personal

Requirement: You must be using a shield

Effect: Until the stance ends, whenever an enemy adjacent to you hits you, you can gain a bonus to AC and Reflex against the attack equal to your Wisdom modifier as an immediate interrupt.

Published in Martial Power 2, page(s) 18.