Personally, I do not believe anyone *will* stop him. I'm buying into the whole "he changed the grip on his forehand" talk. After watching the Barcelona final, it looks awfully flat to me (relatively of course). If he can keep it that flat, holding all other things equal, he will win The Grand Slam.
Personally, over five sets, and on fast hard courts, Murray is the only one who even has a prayer, and I believe an on-form Nadal beats an on-form Murray 10/10 times on any surface. IMO, the Murray-ettes did too successful a job of excusing away the 6-1 6-2 demolition that took place a couple months ago. And lest we forget Wimbledon 2008 as well (perhaps the best match of Nadal's 2008 season and quite a demolition).
Sure he's serving like crap now, but it's still clay season. He'll kick that up a notch come grass, and then