We ended up needing 10 loads of dirt in total to fill up the space inside the blocks. I did not complain as dirt is much cheaper than concrete. After each load of dirt W and one of the sub-contractors used small tractors to compact it. When they were done, Leo had a blast running around in the sand. He would run up one side of the dirt, dive off the edge of the blocks, and run back around to do it all over again.
He needed a short break every now and then.
Finally all of that running wore him out!