it has to do with post count, Rock Stacker being the newest and lowest.. I'm not sure what the actual hierarchy is though, or what comes next.. maybe tree saver?
And to state what may be obvious, the name comes from 4wheeling terms, where someone who stacks rocks is presumed to either not know how to pick lines and/or not have a very built up rig.
82 fj40, 99 uzj100, 06 gx470
05 525EXC, 01 XT225, 09 TTR125, 07 TTR90, 07 CRF50