I am thinking .30-06, it kills everything..right?
I would take a .50 BMG, shoot it in the eye or something.
Funny story, I had a dream the other night. My bed is right next to the window, and I dreamed a Rex was trying to get me. I shot all my 00 buck at him, which failed, then I hit him once with my Glock 23 (.40 S&W) and he dropped like a rock.