Sharks are not an issue for most people unless you spent a great amount of time in shark-infested waters. Divers, professional or even casual, may not even need to use any shark repellent methods, as they do not typically frequent areas of water in which sharks are frequently found. However, an encounter with a shark can be deadly or, at best, extremely devastating to the body and, for those who will be in areas where sharks swim and feed, an effective shark repellent is an absolute necessity.
Sharks are not always as aggressive as they appear to be on TV, however it is possible that a shark may feel threatened by a human presence and will attack. There are some breeds of shark that are naturally aggressive, however, they do not typically attack humans unless provoked or if they are sick or starving. Although most sharks do not come onto beaches or areas frequented by humans, there are many cases each year of swimmers who were not in deep or shark infested waters being attacked.
There are a limited amount of methods that can be effectively used as a shark repellent.
One common way to keep a shark away is to use the power of electricity. SCUBA divers and other underwater swimmers may find success with the use of an electrical field generator that can be attached to the body. This shark repellent will surround the diver or swimmer with an electric fence of sorts that will effect the sensory and neuromuscular systems and repel them from approaching the human or returning to the area while the force is present.
It may be possible to use certain chemical reactions, such as those that occur when pheromones are present, to repel sharks, however, be sure to use the right ones. While certain chemicals will create the need for flight, others may induce the shark's instinct to fight.
As a last resort during a shark attack - try punching the sharks nose.