I have also taken to tying a line from the mast to the dolphin striker bolt immediately below the mast foot. I initially used a separate line, but now use the downhaul lines which are attached to the mastfoot. This is on a Shadow, when dropping the mast solo - the Shadow has no pin (it has some other ingenious design that should prevent the foot jumping off the ball, but I don't trust myself that much). If a pin is meant to be used (as on my Spitfire, Nacra 6, and Dart before that), I'll use the pin. I'm not sure I'd trust a line through the mast foot / ball in the place of a pin (wouldn't it just get cut through???), but I would tie it off externally.