Check out this board for grass called the Turfboard. Instead of wheels there is a caterpillar track system that enables it to go down grass hills. It's like snowboarding, surfing, and skateboarding, except the Turfboard is used on grass.
The Turfboard has a tow cord attached to the front of the board that helps the rider have more control while going down a hill.
Video of the Turfboard in Action

US $2.00