I had some great octopus at a place out near Napa this summer. I asked how they got it so tender. You won't believe this. They put the octopus in a tumbler with golf balls and beat the hell out of it.
So, I'd say head over to the local driving range with your 8-legged friend and sneak him into the ball hopper for a few minutes. If you have a choice, I'd recommend Pro-VI's.