The same thread on SB has drawn quite a bit of interest. Z1taz aside from always having already done what others are coming up with brings some valid points. Specifically about how long and sharp the spike needs to be and possible accidents. I've written about this in a previous thread, in particular note the story where I got the spike jammed into my arm http://spearfishing.world/spea…-spike-for-spearguns.html
I shot a cuda a while back that made some good escape runs. The difference was that I was in shallow water messing around without a float and line. When I have a float I usually let go of the gun and play the cuda from a distance until I know it is spent. I couldn't do this yesterday and consequently was rather quick in trying to handle it before it was spent. I did this by grabbing the mono to bring the fish closer to me. That's when the fish made another run and the mono slipped through my hand. As it was going through my fingers I had a mental image of the speargun getting closer and then "the spike" but it was too late. I got spiked in the left arm. I must've tightened up on the mono instinctively because I stopped the cuda's run, I don't think it was my skin that stopped it as the spike didn't perforate it completely. I imagine it could have been much worse had it been a stronger fish and had it got me in the head. In the future I may put a cap on the spike and keep it there until the moment I need to use it.
BTW to make the shaft removable a screw coming in directly from the back combined with threading at the blunt end of the shaft may do the trick.