Ever since I was a kid

Start a tree-planting campaign and bury the bodies under the trees.

The best way is obviously quicksand.
You don't need to do any burying as it takes care of that itself.
Finding a body in quicksand isn't unexpected.
Whoever does find the body is allready sinking in quicksand and won't be telling nobody.
The only problem is if someone finds the body before it's submerged.

This is what the "smiley face killers" do (Google it)