Even while putting all your efforts towards defense, you are able to parry and counter one of your opponents' attacks.

Prerequisite(s): Combat Expertise, Dangerous Defense, 7th-level duelist

Benefit: Once per round while you are taking a total defense action, you can elect to parry an attack directed at you or an adjacent ally as if you had elected not to take one of your attacks. The parry uses your normal attack bonus. If the parry is successful, you may attempt a riposte with a -4 penalty to the attack roll. You still cannot make other attacks of opportunity.

Normal: Normally you cannot make attacks, parry attempts, or attacks of opportunity while taking a total defense action.