Combat Defense( Player's Handbook II, p. 87)
[Combat Form, Fighter Bonus Feat]
The state of keen focus and mental discipline you attain in combat allows you to shift the focus of your defense from one opponent to another with careful, precise maneuvers.
While you maintain your combat focus, you can change the target of your Dodge feat to a new opponent as an immediate action. If you have three or more combat form feats, you gain an additional +1 dodge bonus to AC against the target of your Dodge feat.
A fighter can select Combat Defense as one of his fighter bonus feats.
Designating or changing the target of your Dodge feat can only be done on your turn as a free action.