Try Aquatic AV. I have a floating remote that the rider ties up to his shorts. I also have an Aquatic AV round remote mounted on the rear of the boat. Aquatic AV is normally used in high end yachts. I knew nothing about this equip until I met a guy that has worked on stereo equipment for 20 years.
In the past 8 years, I have had not one single problem. Here is a link to their website.
I also got my deck from here as well. Good luck