In some areas, curses and spells were inscribed upon thin sheets of clay, rather than metal. They were rolled up and disposed of just like their metal counterparts. Use a block of soft clay, available in craft supply stores. Flatten the block out with a rolling pin, as thin as you can.
Use a nail or a knife to mark your spell upon the clay. Be sure you don’t press too hard – you don’t want to go all the way through. Once you are done writing your spell upon the tablet, roll it up into a tight tube. Dispose of it by burial or one of the other methods described.