Our Automatic Water Bowls have an optional Heavy Duty (HD) cover that are sold separate. They are constructed of marine grade canvas and are tear resistant. They will fit over a Chiller Cover, so will help protect the Chiller Cover from your chewers. Although nothing is guaranteed absolutely safe from a determined canine. HD Covers also help in cold climates. Since they are dark , will absorb any sunlight, and an HD Cover over a Chiller Cover will help resist freezing. Prolonged cold weather will freeze anything, but this definitely helps insulate. Hot Tip: A customer in the Rockies told me on those cold nights he will place a 12 hour hand warmer packet on top of the Critter Cooler, then cover with the Thermal Cover and the HD Cover and that system seems to work well to keep the water from freezing for his huskies.