The company is also working on a chemical repellent, a slightly sweet-smelling combination of a dozen compounds that mimics the scent of rotting shark. Patrick Rice, the senior marine biologist at Shark Defense, has developed the repellent in several forms: as a pressurized can of aerosol spray that can create a 50-milliliter cloud and is popular with spear fishers, a pouch that bursts underwater to quickly clear an area, and a gel that can be injected into bait to keep sharks from getting hooked. The chemical repellent is less expensive than rare-earth magnets. Still, Rice says, "just like anything else, nothing's 100 percent effective. If sharks are in a frenzied state, if they're hungry enough, they'll start eating."