Chew Guard & Bottle Holder www.petco.com - $4.99 (for 16oz. bottle) Product Description: PETCO Chew Guard & Bottle Holder for small animals helps protect your bottles against chewing and destruction from your small animals. Our bottle guard is very easy to use. Simply place your bottle inside of the guard and follow the hanging instructions on the package. Mounts to most wire, wooden or glass habitats. Fits 16 oz. bottles. RattyRat's Review: These bottle guards work well if you need a device to hang your water bottle in an aquarium. Since this bottle holder puts the bottle on the inside of your rats' habitat, the guard part works very well to keep your rats from chewing holes into their water bottle if it happens to be plastic. However, if you keep your rats in a cage, we recommend that you purchase a water bottle that mounts on the outside of the cage instead, because an outside mounted bottle is so much easier to access and refill when needed.