Just put a layer of wax paper right on top of the liquid. That keeps the air out. Or if I am going to use it again, soon, I'll just put a layer of plastic wrap under the lid for a short period of time. I have never had problems doing either. Putting marbles in a half empty can of any liquid would take a lot of marbles. And a mess to clean up if you wanted to save the marbles. I remember Russ saying all of this years ago. But, people have their own ways, I guess. Good luck.