The way we had it house ruled was that if you sacrificed an attack you could add the attack bonus to your AC for one attack. The target you were parrying had to be designated and focused upon, which essentially left you flat-footed for other attacks. An opposed attack (like an opposed grapple) was made to see if you connected with the weapon, and things like catching wrong were reflected by disarmament or dismemberment.<br/><br/>Parrying a creature with a size category greater than yours meant a -4 for both the parry AC bonus and the attack roll for deflection, for creatures<em>your level or lower</em>anything higher level than you incurred a higher penalty to reflect having more combat experience.<br/><br/>Ofcourse this is just observation for what we used and I am not necessarily suggesting it for this game.