Melissa

While you were obviously only making a point with your statement  ". .
.never found a grave with GPR and lots with a backhoe," I fear that it may
be taken literally by the uninitiated.   My reaction has nothing to do with
GPR (never could afford to even rent one) but with the word "backhoe."  If
a sheriff comes to me for help the first question I ask is "have you used a
backhoe?"  If the answer is yes then I tell them that it is too late for
help, they have already disturbed or lost the evidence.

A backhoe shovel can remove a whole burial without anyone ever seeing
it.  The power equipment of choice is a grader (road patrol, scraper, etc,)
or a well controlled bulldozer with an experienced operator.  The bulldozer
should be medium sized (Cat D4 or IH TD9) and with hydraulic controls not
cable.  A front-end-loader, usually on the other end of a backhoe, cannot
be controlled well enough to be considered.

The difference should be obvious to an archaeologist; backhoes take out
chunks while graders take off "lifts" as small as under an inch.  This is
not based on theory but on experience with prehistoric, historic, and
forensic excavations.  A sheriff can usually get the desired equipment and
experienced operator from the county road crew in minutes.  Mass graves in
your experience may be an exception once they are found and need to be
exposed at the margins.  An  experimental excavation with different
equipment might make a nice MA thesis.

Rick