Fill the balls up with piss tape em up and bombs away!!!
I've read a few of your posts, and I have to ask you, are you just screwing with us to see our reaction, or do you have some sort of mental disability? Because the few of you posts that are actually composed of coherent English are either horrible ideas, or pure bullsh*t.
As for pingpong balls, a ball filled with powdered/finely chopped lead or steel, and then injected with liquid epoxy to seal the cracks, could be relatively dense while being reusable.