I couldn't go through all 16 pages of posting, so forgive me if this has been discussed, but there is a knife out there called the WASP Injection knife. I believe it was meant for divers, but I'd imagine it would work well on any large predator. It has a CO2 canister in the handle and an internal channel that runs to the tip of the knife. Press the button and a basketball sized cavity of air is instantly injected. I would imagine that would instantly stop the heart of a bear or mountain lion with the right placement. Their site is called waspknife.com.
Here's a video of them testing it on a watermelon...fairly impressive:
[video=youtube;Sa_NC-_fvKs]http://www.youtube.com/watch?v=Sa_NC-_fvKs[/video]