I’m guessing amateur fireworks are quite illegal here in Indiana. Now, I have shot a 2-liter bottle of soda before with spectacular results, but I am thinking it would be less than dynamic with a watermelon. What I am really going for here is some sort of mass destruction of the melon. Any kinds of suggestions are welcomed.
Get a small plastic bottle with a screw-on lid (like a pop bottle). Add a little water, throw the dry ice in and secure the lid. Insert bottle into fruit (carve out a hole beforehand).
The dry-ice-in-bottle method makes really nice explosions.