Shark attack!
If while swimming a shark swims rather close to you, piss yourself.
They find the smell incredibly repulsive and will swim away.
Or, as a mate in the pub said, you could: "Grab a nearby fish, cut it, and the shark will attack that as the blood smell would be stronger and more appealing." Where you're going to get the knife from, or why a fish is swimming next to you, I have no clue.
(greenycrimson I stole the from pyschotherapist, Sun 11 Mar 2007, 16:03, Reply)