We only used fake eggs (golf balls) in the nest boxes to teach the girls where to lay their eggs. Once the girls began laying in the boxes, the golf balls were removed, for good.
I don't have any golf balls handy, nor did I want to buy them. I added speckled plastic easter eggs to our nests instead. My daughter put a few rocks in each one for weight. They finally started using the nests instead of the floor of the coop after that.