I have a similar one made by Unipet. Where the S crew goes through has a hexagonal shape to it and the base of the s crew has the same shape so it cannot be twisted and has a wing nut on the outside. It is about the only one I found that the Cockies can't throw the bowl part out and have great difficulty twisting so that it cannot be tipped upside down. It is very heavy grade plastic and they don't tend to chew it either. Unfortunately the company that was supplying it in Australia has stopped stocking it and we are trying to find a new distributor for them.