I am still waiting to see how you get worms to surace
with a hand cranked Megger.  Would it be better to use
Megger directly on the fish in the water?
  <Very evil grin and laughter>
With my luck all I would catch is a Game Warden!
 Actually the more common use for a megohmmeter in
checking "ground" is checking ESD (Electro Static
Discharge) disapative work surfaces.  In some cases
it is easier to connect one end of the tester to the
common ground while using the other lead, usually
attached to a flat 5 pound probe, to test the work
surfaces.  Again, the test is not for ground, but to
check that the work surfaces are both disapative and
connected to ground.
As far as checking for dielectric breakdown the more
prevalent instrument for testing is a current limited
"hi-pot" (High potential).  High voltage is the
mechanism causing the dielectric breakdown. Current
provides the "sizzle"; That is why you current limit
the instrument to, oh, somewhere around 50 to 100
microamps.
For ground testing the Power Co. around here uses
a low ohm tester.  Basically an ohmeter that actually
measures th IR drop between two grounds.
RF grounding is opening up a new can of worms...
Now about those worms...  I am ready to go fishing!
I hope that this has helped to eschew obfuscation!
         73,  Cal K4JSR