Just my 2 cents worth...in our event the pit has a simple trap door hinged on one side, anyone falling in the pit will find himself about 2.5 feet below the arena, the pit has no sidewalls so if you move or roll to one side it will be next to impossible to get out of it, even for a flipper as you'll hit the pit ceiling trying to get out. Imho it is the simplest way to build it and the biggest chance who falls stays there