Well I got the magnets that hold up to 60lbs and it does hold the rock better but I was hoping it would be a little stronger. I'm guessing the magnet in the rock needs to be stronger too. Anyway, it works and I have the rock where I want it now.
I found a local guy with a tile saw that will cut my rock for me. Now I need to get some epoxy and more magnets so I can make me some more "clouds"!