My course uses a counterweight and subfloat that is essentially the opposite of the diagram @PhatTony showed (a counterweight instead of the subfloat[here in the frozen north, muskrats will eat the foam subfloats]). The counterweights are just red solo cups filled with concrete attached to a screw anchor on the bottom that go through a loop on the buoy. Since ours is in slightly deeper water, we use a subfloat, but if it's shallow there's no need. Similar to @PhatTony's setup, at some point of shallow water, the counterweights will hit the bottom, but as long as it's deep enough to ski, that shouldn't be an issue...