Keeping your fishing line tight in wind, current, and more requires proper line attachment and correct drag setting on the reel. Regularly changing line, right lure weight, correct lure position, casting downwind, casting with the current, and keeping excess line off the reel as short as possible.
There have been 50 unprovoked shark attacks on kayaks since worldwide records began in 1779. This is less than 1% of the total shark attacks on humans. 5 of these attacks have proved fatal, there is a limited risk of shark attack on fishing kayaks, however there are steps you can take to reduce that further.