I find hidden nests all the time. Here's a little trick I've learned. If I clean out the nest and take all the eggs - they usually won't lay there again and will go hide another nest. But, if I leave a couple of eggs, they will continue to lay there and I will know where to find them. So what I do (when I first find a nest and don't know how old the eggs are) is to take all eggs out and add them to bucket of eggs that get cooked and fed back to chickens. Then I put a couple of fresh eggs, from that day that I've gathered from the regular nests, into the "hidden" nest. Then each day I continue to gather the fresh eggs in the hidden nest always leaving two.