A relation of mine uses one og those electronic insect repellers. Plug it into a power point and it causes the wiring in the house to emit a sound that mice and bugs can't tolerate, much like the electronic roo shoo.
If it were possible to produce a sound that sharks can't tolerate then whats the problem with mounting the device on a buoy permanently. Popular beaches and surfing spots could have these devices spread offshore and allow reasonable safe use.
