...slip on the powerhead and get ready to pop him.
You know, when I was relatively new to spearfishing and I found out about Tito's affordable powerheads, I bought a whole bunch, thinking I'd be using them on a regular basis. However, in reality I've never felt threatened enough to feel compelled to slip one on. The few occasion where I did feel threatened, I simply didn't have the chance to slip it on, as the shark caught me totally by surprise.
It seems like on most occasions as soon as they know they've lost the element of surprise, they aren't as brave and keep a bigger distance. Although his tends to change when they are in a pack or fresh fish is involved, but even then its not guaranteed. I shot a yellowjack of the back of a bullshark during Nationals a few years ago, it was a spine shot that sent the fish in a vibrator like dance with blood gushing from its gills. I had been dreading this scenario, but to my surprise, the shark didn't even turn around to look at me. Just leisurely swam along. Go figure...
I've witnessed several sharks get shot, but I am of the opinion that more than likely a jab with a shaft would have deterred the shark just fine. I think that if you're in the water, and a shark shows up whose behavior you don't like, you should move spots, not pre-emptively kill it when it make an inquisitive close pass. Often people mistake curiosity for aggression. In most cases people have plenty of time to get on the boat. Anyways, I'm not a shark hugger, but I respect them, a respect they have definitely earned.