If we are going to dig a hole we need to take a concrete fence post or steel girder with us (I've go both in my garage) so that we can exert some forces on the chalk and see how it reacts. An A-frame, a piece of rope, a large bucket and something heavy to fill it with (water?) would enable some accurate enough measurements to be made. We don't need a very deep hole - I want to see is how much strain is needed to break the chalk and I can then scale it all up for the big one. The sooner it breaks, the less work will be needed and the sooner we can all go home again, though it would be nice to see the BBC's trilithon while we are down there.