I had thought about putting a 1/2 inch thick steel plate on top of the face but I know that if the two surfaces are not completely smoothe and flat it will cause an air space to exist between the two surfaces and dampen the rebound. Since I have two of these stones carved, I think I will experiment with the larger one (160#) by using a ceramic tile mortar to fuse the metal plate to the face of the anvil and see how dampened the rebound is. Of course I will put the mortar on the steel plate and then lay the rock on top of the steel plate so that there is plenty of weight on the mortar to squeeze out excess mortar and air bubbles. This should be fun!
I will keep you posted on my results.
-mike-