Portee,

you are wrong about that rock, it must be a meteriorite with a direct hit. Or the other possibility is that it is pure gold and the only way to keep it safe is to keep it in one piece so no one runs away with it.

When I lived in Chile I saw this train loaded with copper, it must have been 100 million dollars of worth of copper on that train. Of course stealing it is another matter, you would have needed a lot of heavy trucks, and where do you drive? So yes, no guards!