The track for the skateboard would be a single rail track on ground level, built in sections and fastened to the ground over a sloping terrain. The rail would be hollow consisting of a chamber to house both wheels of a skateboard. The skateboard would consist of a typical platform for the rider and have a single wheel fore and aft. The skateboard would essentially be locked onto the track, yet freely move at potentially high speeds- depending on the length and slope of the track. We're talking extreme sport here!... as an advanced course might consist of an alpine run starting at the top of a mountain and ending in a valley below. Helmet and other protective gear highly recommended. Or how about a bobsled version to prevent the rider from falling off?
Reward: Install a baby one in my backyard.