A fellow by the name of killaseahorse on SB made a double trigger speargun. The idea is that a long gun can be used as a hole gun. I've ran into this problem a few times with my long gun, this is a possible solution. I like to keep thing simple so my first reaction is against it. But it's an interesting concept. Maybe more applicable to scuba? The secondary handle can be quite a bit smaller as you'd normally power down a band and there wouldn't be so much recoil. It could also have a safety which I normally don't have on my gun.

