Get a waterproof sleeping bag and bury the person head first feet up. Pull out the teeth, clip off the finger tips and toes and put them in a 2lt bottle of coke and stick it at the bottom with the head. As the body decomposes the liquids of delicious human goo will condense at the bottom of the bag(in the head, making facial recognition impossible without computer reconstruction) and the coke will degrade the finger tips/toes and teeth making identity by finger prints and dental records impossible. After a while the bottle of coke will explode from pressure built up by the fluids from the body parts and further degrade the body because of liquidation, even the bones will eventually get warped because of the coke. Nothing will leak out because you're using a waterproof sleeping bag and after a few weeks of decomp the entire body will be a gooey pile of human goo at the bottom of a small sleeping bag and as this all happens the dirt will slowly sink making the hole look natural because it will remove any marks that it was dug.