A question I should have asked yesterday

[Cbad Mike]

Today I finally hooked a nice halibut. 1st good on from my kayak! It freaked out when it saw the net so since I knew that I wanted to keep it I used my gaff and pulled it onto the kayak. The hook came out when I got it on deck. I quickly snapped a photo of dinner and then realized that I needed to kill it. During the FOURTH stab in through the head it freaked out, tried to bite me, and then jumped back in the water and swam away.
I feel like a f#cking idiot!! I've landed plenty of fish in boats and on docks where the fish had no where to go but am new to kayak fishing.
So the question that I should have asked yesterday before I caught it is what is the best way to kill a halibut quickly so it doesn't bite my junk or worse yet, jump back in the water like today? Just to plan ahead this time, maybe I can add the same question for other types of fish too?
Thanks,
Mike