If they are those fiberglass ones, get them in the ground and then bend or crush the likely area where they are pulling them out. If they pull them out barehanded, they'll end with a hand full of fiberglass splinters.
I use the fiberglass ones in my yard as the plow can still wing the bank back and the poles snap back up. Rebar does not, and the plow drivers get grouchy (technically, where I use them is the right of way).
With the wear over the years from being winged over, I don't grab them bare handed anymore either. Learned my lesson the hard way.