I think the combo of GPS and Metal Detector with metal markers would work well to mark them, but it would be somewhat of a pain to do that, and then have to return to the location later on if the market does what you want it to.
If you marked them and the market did not rise to meet your sell price, suppose you could just leave your markers in place and could locate them the next season if the market does what you want and well if some joker does not dig them before you get back to them.
Some of the places I hunt, are quite remote and walking in there one time is quite a task, making another trip would double that task.
It can also be quite difficult to locate a seng root (at times) if the top is not attached. I have had the top break off on me on some of those late fall plants and then dug a hole as big as a basketball and could not find the root anywhere.
If you marked plants in the summer or fall, and the market was so so until January, Febuary and then zoomed up - well you might be digging a lot of basketball sized holes wondering where in the heck is that root
Good Luck !
TNhunter