Cumbrous Dodge( Savage Species, p. 31)
You have a chance to dodge attacks that hit you, but at a cost.
Tumble 4 ranks,
You may activate this feat as a free action. You gain a +2 bonus to your Armor Class for the rest of the current encounter. At the end of the encounter, you are fatigued. For details on fatigue, see the Condition Summary in Chapter 3 of the DUNGEON MASTER's Guide.