I’ve made my own, they aren’t as fancy as the BB ones though (which I’ve also bought, and are awesome). I ended up making my own once our pet sitter accidentally threw away our BB one!
You’ll want to hardware cloth, I believe the grid size is 1/4″ (so it’s smaller than you’re bun’s poops!).
I cut a piece slightly larger than the litter box, then fold the edges under (so that a couple rows are folded under), then fold the corners under. It might take some adjusting to get it to fit your box, so don’t fold the edges completely flat until you are happy with the size. Make sure to use small enough wire cutters to trim any sharp parts really well. It’s really important that there are no sharp edges or pokey wires that could hurt your bun. You should be able to run your hand smoothly over the whole thing and not feel anything sharp.
Also be sure to inspect it regularly when you clean the box. The corners where it’s folded can have wires break and start poking up. Usually you can just trim these down and you will be good to go.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.