They make a cable clamp that you could secure it with but in your case you might consider getting a crimping tool and crimp a clamp on, a lot less chance of getting scratched up on when in the water, also the coated stainless steel cable will last indefinitely in the water and be a lot smoother if you came in contact with it underwater.
Also the breaking strength of it is pretty high, my theory is a 3/16' to 1/4" cable would anchor something in place pretty well.

All the really good ideas I've ever had came to me while I was milking a cow.