: Ask Shawn, I've seen him roll with a rock about as big as a soccer ball 
It's a parlor trick.
The secret is to keep the rock very close to your body throughout the roll, and only do a fast sweep with your arm/rock at the very end--when you're almost all the way up.
It looks like you're sweeping with the rock the entire roll, but if you do that, it acts like a "bulb keel", and pulls you straight down.
I can only do that one when it "doesn't count". I tried 3 times at the SSTIKS rolling demo/contest, and failed them all.
And the Middle Fork is running great, so I honestly haven't even had a GP in my hands since SSTIKS. And the Gorge tomorrow...and maybe the North Fork next week!
Shawn
