The only reason a stone would be cracking or exploding is because the item placed on it is cold. Whether it is fresh or frozen pizza, you should let it get to (at least)room temperature before putting it on the stone. This can take time with frozen pizza, so what I do sometimes is take a long sheet of foil, fold it over 3-4 times, oil it lightly, place the frozen pie on it, and then put it directly on a stovetop burner, put it on high for about 10-15 seconds. Repeat 4-5 times, just to get the chill out of the crust, and that should do the trick.