Active Shield Defense( Player's Handbook II, p. 71)
[Fighter Bonus Feat, General]
Your expert use of your shield allows you to strike at vulnerable foes even when you forgo your own attacks in favor of defense.
Shield Specialization (PH2) , Proficiency with shields,
When fighting defensively and using a shield, you do not take the standard fighting defensively penalties on attacks of opportunity. When using the total defense action and a shield, you still threaten the area around you as normal. You can make attacks of opportunity with a -4 penalty.
A fighter can select Active Shield Defense as one of his fighter bonus feats.
You take a -4 penalty on all attacks while fighting defensively. You cannot attack while using the total defense action.