It's been subject to some whine that monks don't have riposte. Well, howabout
changing joint lock so that you have a (smallish) chance of applying a joint
lock after parrying a hit that would affect the monster capabilities in
similar fashion to stun? (for example, duration variable from 1 to 6 rounds,
effects from decreased defense to decreased attacks...). This, I believe,
would suit the idea of monks much better than your ordinary 'I parry then I
hit you back'-approach with riposte.
Then again, there maybe a reason why monks don't retaliate in any way after
parrying..