I have a row of 24 2'x2'x4' limestone blocks on which one side of a deck anchored to the top. We've had a wet spring and lately I've noticed mildew on the side of the boulders and the limestone seems to be cracking/peeling on the front. I can also see some smaller cracks on top, which looks like will also cause further cracking on the front face. My first thought to fix this would be to use a stone sealer to inhibit mildew growth and prohibit water from getting into the cracks. Are there any other better sollutions? I want to do something before these boulders can't support my deck anymore.