SRD:Defending

Defending: A defending weapon allows the wielder to transfer some or all of the sword’s enhancement bonus to his AC as a bonus that stacks with all others. As a free action, the wielder chooses how to allocate the weapon’s enhancement bonus at the start of his turn before using the weapon, and the effect to AC lasts until his next turn.

Moderate abjuration; CL 8th; Craft Magical Arms and Armor, shield or shield of faith; Price +1 bonus.