A pizza fence has a raised circular ring with downturned legs and equally placed divisions running through the center to the edge. It's placed over a pizza before being sliced.
In between each division is a groove where a pizza wheel can be inserted to cut perfectly straight lines. They are a stable guide for the blade and make it impossible to deviate.
The pizza fence has handles on either side and a large radius, which makes it big enough to sit over the top of an entire 18-inch Costco pizza without disturbing the toppings.