Well Amos I have experienced dirt loss (as well as dirt expansion)and we didn't lose any of it due to it getting lost in grass or weeds. It was all scraped off of a concrete slab and back into the hole we dug and we came up short on several occasions. Other people down here have said the same thing and they all blamed it on the moon phase too.

Murray, bring yore shovel down here to Palm Beach County and I'll show you where you can get started;~) We jet 24' long well points down prior to excavating to install fuel storage tanks and never touch a rock. Out around Belle Glade and Pahokee the cap is only about 6-8 feet down. Everything on top out there is black muck though and grows sugar cane and sweet corn pretty good.