I just use a spare ceramic floor tile, ( you know the ones you have left over from the flooring job and always keep "just in case you need to replace a tile" ) upside down so I cook on the unglazed side.
What I do is:
1. Heat oven to about 200C
2. Put in tile and turn on the grill. Grill the tile for about 20 mins. In my oven the grill turns off the oven and its fan
3. Pop in Pizza and turn oven back to max wack
4. Cook for 10 mins ( depending ) remove pizza, re-grill the tile for say 5 mins then put back pizza and grill off the toppings
So far have only cracked 1 tile ( after about 20 pizzas ) but hey its a floor tile!
Will