Then throw some dirt on top and 'discover' it anew during the harvest? If something has been there for hundreds or even thousands of years it can probably last another few months. Not really a workable solution for construction, but surely a farmer might get away with it? Or one might store a found object for a while before realising it's historical significance.
But you might still be in violation of the law. There's also the problem that the investigation on the land might take a lot longer than just a couple of months. We had an archaeological finding in our city that took several years before they could use the land again.