You can really reduce the current shark repellent/deterrent technologies into three categories: visual, odorous (smell) and electrical. We’re going to briefly break those down for you (because you could literally get a PHD studying any of these). There’s a ton of foundational biology that is behind these technologies, but we’re not here to teach Elasmobranchs 101 here. For an outstanding paper on the many sensory abilities of sharks please.