“The trick is to dig it extra deep, and put something non-incriminating down about six feet. That looks like all there is in the hole. Y’know, I’ve heard. ;^)”
Plant tomatoes or some other lovely aromatic plants over the spot. Nobody will dare dig it up or disturb it, right? And tomatoes have a very strong, distinctive aroma.
Typically the first thing found is regarded as the bottom of the hole. I think I saw this on an old detective show episode, maybe Columbo.