In the Boy Scout manual they show a few different fires that you can build depending on the need at hand. There's the log cabin fire, V-fire, the trench fire, the tee pee fire, the reflector fire, and even an elevated fire (built on a platform covered with about a 6 – 8 inch layer of dirt). The platform keeps the fire off the wet ground and the dirt keeps the platform from catching on fire.
Doctor Hoylman, my old Scoutmaster, made us all build our cooking fires 'in' the ground. We saved the dirt to fill the hole back in and replanted the sod so the ground could heal itself. We/he called it a keyhole fire but later on I found that is really a modified combination of a trench fire and a keyhole fire – a keyhole fire according to the book is on top of the ground and it is designed using rocks laid out in the shape of a keyhole in a cleared spot on top of the ground. This is to contain the fire and not let it spread.
First we dug a round hole about two feet across and about a foot deep. Next we dug a rectangle hole connected to the round hole. This gives it the shape of a keyhole thus it's name. The purpose of the round hole is to contain the fire and to prepare the hot coals for cooking. You rake hot coals from the big fire over into the rectangle shaped hole for cooking since you should never cook over open flames. Throw an old refrigerator shelf, stove grate, or a store bought grate on the rectangle hole and you are ready to make hot coffee or fry up a mess of potatoes.
I've noticed that at most Mountain man rendezvous and Civil War reenactments they cook over the modified keyhole fire. The next time you camp where fire pits or grates aren't provided try using the modified keyhole fire and I think you'll not go back to using a fire on top of the ground again. I know Mother Nature will be happy.