Really, it's difficult to render anything still in one piece inoperable. I know of a guy who bought an ornamental cannon. He used a gouging rod to remove the plug that was welded in the barrel. Then used a jackhammer to get the concrete out of the barrel. I have never seen this cannon with my own eyes but from what I hear he got it to fire. The things people will do with tools and a little free time never ceases to amaze me.