Use diamond and wall. :0

Add sponge use console to type in: set life spng 9999999999999999999999999999999999999999999999999999999999999

That will create a layer that will take ages to destroy with heat based weapons, add a layer of bizarre solid. The heat required to burn the sponge will strengthen the bizarre.

Also, if you create a layer of lava that will cool down after a certain layer is destroyed and use console to type in: set ctype lava dmnd; You wouldn't technically be cheating as there is wasn't any diamond to begin with.