The fender of a truck, or the hitch will also work. I don't remember what device
you were talking about. I'd just hate to hear that the boat got away from you
while you were backing it into a parking space downhill.

Good tip! The truck will almost certainly be nearby when I need to
man-handle the boat/trailer into its parking space. This means I
should have no problem wrapping a rope around the tow-hitch-ball in the
truck.

Thanks.

Jay Chan