My grandfather installed a anti-plow device to keep the planter he made out of brick that housed our mailbox pole...dug two holes in the ground, sleeved it with plastic and had a heavy cast iron u-shaped pipe he put into the holes. Never had a problem with the planter being wiped out again!
Of course, never did come up with a good solution for getting rid of the Himalaya's left by the plow guy! Well, other than me!