Urinating in a wet suit will leave a trail of urine for quite a long time as the urine first leaves the wetsuit in signifcant volume and then as traces are rinsed out of it . . . Shark attacks are quite rare, but it's not a good idea to tempt fate.
I remember jamie & adam trying to bust this myth on one of their specials during shark week. first of all lemon sharks are not interested in our urine, second of all, their sense of smell is not that acute, they can't smell a drop of blood from a mile away.
Warning -- they only used lemon sharks, results may differ with great whites