Here's my solution to filming with a GoPro when sea kayaking - a mouth mount / bite mount - whichever you like to call it. Often when I'm kayaking I'm not wearing a helmet so can't use that to mount a GoPro. Commercial versions are available but this solution is ultra cheap and has some advantages. It's made from a piece of plastic kitchen chopping board, shaped to suit, with a standard GoPro mount plus stainless steel screws and bolts. Pop it in your mouth and bite on the plastic and you can easily breathe at the same time. I can just about see the rear screen of the GoPro which is useful if you want to point out something and you can see where your finger is relative to what the camera is filming. When not in use it can sit in the top of your buoyancy aid or just dangle on the rope (with float) around your neck. The only downside is that your breathing gets recorded on the GoPro !