Okay...I am the worst when it comes to NOT breaking a nail. I seem to always have at least one nail that is tearing or peeling at all times.
I've yet to try this, but Colette at My Simple Pleasures has a wonderful tutorial on her blog. If you have the same problem as me you have to check out Colette's post here:
I would also like to note that I think she is the queen of water marbling. Whenever I'm awing her video guides, my husband even likes to watch them.