Point board downhill, grab sack, ride.
I don't know man. Are you putting too much weight on your front foot and the back of the board is getting squirrely as a result? About the only thing I can think of right off the top of my head.
"People say that marijuana smoking is going to get in the way of my career. I say to them that on the contrary, my fighting career is getting in the way of my marijuana smoking." -Nick Diaz