Highly Recommend buying a GoPro.
I own two GoPro's, a Hero 4 Black and a Hero 3+ Black which both take incredible footage and are super simple to use.
I use the GoPro Head mount which you can just put on under your wetsuit hood and away you go!
You could also use a tripod mount and mount it onto your gun if you prefer that style of footage.
You can download the GoPro Studio Software from the GoPro website which makes editing videos a breeze!www.youtube.com/360spearo
- Check out my videos all filmed with the Hero 3 Black and Hero 3+ Black.
Only just picked up my Hero 4 so havent got enough footage for a video yet!