Divine Defiance

 
Prerequisite(s): Ability to Turn/Rebuke Undead, caster level 3+
 
Benefit: You can spend one of your turn/rebuke undead attempts as an immediate action to counter a spell or spell-like effect. You must have the relevant spell prepared as normal (or dispel magic), and you must make a spellcraft check to identify the target's spell if applicable.
 
Source: Fiendish Codex II