how big a tank? you might look into getting some pink foam insulation, and placing it under the glass, inside the bottom rim/trim, to help spread the weight of the tank evenly.
It sounds like the way the live rock was stacked, that it was putting a lot of pressure on one spot, and eventually, it fractured. It is possible the glass had an imperfection though.
Since I have a 40gallon breeder, it has a larger footprint, roughly 36"x18", and no center brace.
What I did was took that foam insulation, and made little 3"x3" squares, and just staggered them down the center of the tank, and making sure that they were actually about 1/16th inch thinner than the space they filled. This allows the glass to bow a little, which it wants to do naturally, and ensures that i'm not putting extra pressure on a certain part of the tank.
I couldn't get the exact thickness, so that's why I made little supports, rather than one large pad to span the entire 36x18. If I had a hot-knife, I could have done that easily, but I don't.
Former advisor and planted tank geek...life's moved on though.