I avoid the whole hoop-holding question by using a lap hoop. Here is a picture of the one I love:
http://www.keepsakequilting.com/prod...APTOP-HOOP.htm
It sits in my lap so both hands are free for the rocking motion.
Are you hooping your quilt loosely? I was told to have about a fist-width of "give" in the hoop. Beginning quilters often think the quilt is supposed to be drum-tight.