Do sharks (or other sea predators) respond to sonar? Is this more likely to make you prey or would it actually help with annoying them away?
And dolphins and co. are sensitive to sonar and you would likely drive them away. Sharks not so much. But I lack detail knowledge.
https://www.hakaimagazine.com/news/many-shark-repellents-don...
And some of them magnetic, similar to those anti-nausea magnet bands. Some of them work, some don't.
Just waiting for someone with a magnet on their ankle to get it bitten off and sue the manufacturer...