The best solution I know of is to get three-link segments of chain and put one on each screw as it goes into the ground. That not only marks the spot, it also gives you a flexible attachment point which is useful in all sorts of situations. (Two links would be pinned in a stationary fashion.)
Biggest problem is it’s a pain in the ass to chop up all that chain, and nobody sells them in pre-cut lengths.
Biggest problem is it’s a pain in the ass to chop up all that chain, and nobody sells them in pre-cut lengths.