Running Flash and Ghost....
If they slam W then E immedialtely they can fire the stun from far away then just R Q R R Q... one time i had to ghost and E one more time. and flash away from turret but if you are allowed normal farming he has a really REALLY good mid game.
the W -> E may be a glitch cuz firing the stun twice as far can't be done if you are in W and try to use E later. You have to tap W and while he's charging pick a target with E, once he initiates the charge up on W he launches E WAY far.
after learning this I quickly realized the best thing against xerath is the merc treads.
I've played about 12 games with him and im no pro nor am i even dominating with him, but I haven't gone negative. Check stats in Sig.