Was wandering across a heavily disturbed area, full of weeds, and rough stones, and saw a nice round river rock, about 40cms across. A bit intrigued because it was out of place, I gave it a bit of a shove. It fell over on it's back. It wasn't a rock, it seemed to be a hollow metal object, shaped i think to impersonate a rock. It was very realistic. The only thing I can think of is a geocache. Sadly for the placers, the ants thought it was just a lovely house. I replaced it. Co-ordinates didn't come out on the map, but I can go back to the photos, and see if it's come though there, if anyone really wants it :-) but I think it belongs to the ants now.