I use a Kodak Playsport, but same advice holds. This past summer I attached mine to a mini tripod (REI), then secured it under a strap on my drybox in front of me. I could easily reach it to turn it on & off. Videos were pretty nice, but as Mogur said, you get whatever view your boat is pointed at. I'm working on a helmet mount for next summer so I can get better shots. I found a great tether at a fly fishing shop. It's a fishing net tether with clips on both ends. It's coiled so it's not too loose, but stretches as needed.
Maybe Alex will chime in. He fashioned a tripod set-up for the back of his boat to get great POV shots. He will definitely tell you to secure your camera with a tether, as he has one GoPro at the bottom of the river in Westwater.