A shallow grave in woodland, one shovel of quicklime spread evenly over the corpse, it is down to a skeleton within ten days and a few small bones after 4 months. Now if you want to be creative, a commercial bone grinding machine only costs about £300 used, cut the body into small chunks, separated at the joints, then grind it up with strong bleach as this will destabilise dna, any metal implants can be removed and smelted down, given that you now have access to them, wash it all down a drain. Then the old favourite, get a metal locker, drill a few holes in it, stuff the body into it and sink it in a large body of water, all sorts of critters will do the job for you.