I made this for a server, but I figured I should share it here as well.  There's really not a lot to it, it just makes it so that any one block thick dirt or grass falls when you walk on it, like in TerraFirmaCraft for those of you that are familier. It's a tiny 3*3*3 MCEdit schematic that you can just paste into your world.  It's fast enough that if your computer is running well, you still take 80% of the damage you would have taken falling the whole way.  If the clock isn't working, which you can test by walking over thin dirt, you need to trigger the bottom block, then the top one to restart.