I bought two of those Everlasting treat balls, the small blue ones. While there was no damage at all to the ball itself, Izzy was able to remove the treat and OMG is it MESSY
I had to change their futon sheets after that one. It's fine for Luna, she's not a heavy chewer, but Izzy is an extremely heavy chewer. She can finish a bully stick in a couple of hours, while Luna's lasts for days or until Iz steals it
I'd love to find something for Izzy that's safe and will last a long time