Well about 200 feet from my house is a big 'ol river, so I'm guessing the hole would fill pretty quickly with water, no?
I wonder if you could build one up? cinder block walls with dirt piled all around them maybe. then the hog in the pooka, blankets leaves dirt etc on top?
You can do this and I've done it like this a few times. You can build up the cinder blocks, put a layer of dirt (about 3-5 inches), add a layer of large rocks (lava rocks are great) and build your fire on top of the rocks. Keep building the fire for about 2 hours to get the rocks good and hot and so that you have an ample amount of coals. I like to use mesquite wood for kalua pork and will put a few split logs in just before placing the hog in the pit.
After seasoning the hog, we halve some cabbage heads and stuff inside the hog along with a few of the hot rocks from the pit. We then wrap the hog in banana leaves, close the hog and wrap in chick wire or chain link fencing (this really helps in getting the hog out of the pit). We place the hog on top of the mesquite logs and cover in some wet burlap sacks. We then cover w/ some scrap sheet metal (although I've seen others us plywood, metal siding, etc...) and add a few bricks to help keep the top on.
Takes a 60lb hog about 14 hours or so to cook. It's been a while since I've done it this way, so going off memory and I hope I didn't skip any steps, but this should give you a general idea. You could wrap the hog in some wet burlap then cover w/ some dirt to make it more like a traditional imu, but I've never done it this way. The other cinder block pits I've done were more of an offset smoker type style where we didn't wrap the hog in banana leaves and left the hog open. Fun thing is there is no one right way to roast a whole hog and it's a lot easier than most people think!