This construction makes a very stable float marker that doesn't drift and isn't affected by waves. Because the rope can slide up and down and the marker is kept above water by the float underwater, it can self adjust. The adjusting stopper on the underwater float is the same type that's used in clothing to keep drawstrings in place. Select a rope that will easily fit inside one of these clips. The anchor can be made by pouring concrete into a suitable plastic tub.  Cut a slot in the underwater float. Wrap any excess cord around the float and put the last bit through the slot (much like sewing machine thread on wooden cores). This prevents the tangling of the cord in paddles.