The refrigerators and money crate shouldn't be a problem at all. I know Bob failed occasionally when he tried to hide in a huge cabinet on zm_lila_panic_beach. The only one that I think that would be worth any mention is the heavy vending machine shown in Chef's screenshot of zm_retard. Everything else I think I've seen failed at one point or another. Except for that one on retard, I've yet to see a human lose with that one. The location of the heavy prop is superior to the others because the others have huge spaces on top for multiple zombies to push. But in retard, there isn't any space to get on top, and zombies can only approach it from the front and not full circle. However, there is the isolation variable, as zombies tend to not look in that reclusive corner on retard until there's 1:30-1:00 left in the round and thus receives little action