My building site is in the middle of a 50 acre tract of Missouri Ozarks timber.  Geology is typically 6 feet of rocky soil over sandstone and limestone with a few outcroppings of rock.

I've read about vertical loops and slinkys, but with plenty of ground, wouldn't the simplest solution be a big circle of straight pipe buried as deep as I can get it?  A trencher (Ditch-Witch) would make quick work of burying the pipe.  The phone company buried their cable to the site with a little walk-behind trencher, although they only went down about 2-3 feet.

Thanks!

Yes, straight pipe can be used in a trench loop. You'll need to go deeper than 3 feet, though. 6' deep may be deep enough. Most importantly, though, is that you'll want the system sized and designed to the conditions of your site/building.