Hydraulic rototiller in action.  Man, could that baby pulverize dirt and shoot out rocks!  As you can see from the look on my face, it took a bit of strength to keep it under control.  I rototilled the entire backyard to mix the new dirt with the old, unearth all the rocks, and help us fine tune the leveling.  We ended up with a pile of rocks (that we dumped behind the fence) that was four feet tall.