Hey, cool stuff. I'm putting one in my backyard too, as well as replacing a lot of grass with stone and indigenous low-water plants. I recently finished the foundation and leveling that thing was a pain. Had to make a perimeter around it, then use a long board across the frame with plywood attached, to drag it across and level.
Now it looks like I have a Kumite ring back there and a ridiculous amount of fill dirt that I have no idea what to do with. I tried to give it away on craigslist, to save myself the trouble of transporting it. I had a middle-aged woman with a van show up, back it up to my fence, then literally shovel dirt into the back of her vehicle. Keep in mind, I said van, not truck, so this shit is literally just like on top of her seats that she folded down and filling up the entire back half of it.
I asked her why she needed all this dirt and she said that her dogs were digging holes in her backyard. My girlfriend asked her, "Well, if they're digging, shouldn't the dirt still be there, just moved"? We uh, we really didn't get a response to that.
Now I have slightly less fill dirt and some major trepidation towards telling anyone else on craigslist where I live.