The only thing I’ve considered that would be relatively neat is to use small pebbles. Like smooth river pebbles as you could wash them if they get peed on. I haven’t been able to find a large quantity to try this out. I do expect my rabbits would turn it into a toilet and I’d tire pretty quickly of having to wash it and est it up again.

What about using a large box wigh smallish side entrance? She’d have to hop in to dig and the material would be contained mostly in the box. Even a pile of the wood pellets and if it got soiled, you could remove those bits as needed. Or do you think they’d both take to using this as their main litter box?

If you do decide to use dirt, be careful about parasites and such. Im not really sure how you would avoid it? Buying dirt from a store might mean chemicals that are usually used to enhance growth, i dont know if these would be harmful or not, but it might be something to be aware of. If you dig it up from somewhere, you may end up with parasites or ringworm (a fungus that can be found in the dirt). I wonder if you could bake the dirt in the oven for a while to kill anything off and sterilize it.
Perhaps I am being an overprotective nut job but ive considered doing the same and that was what I thought about.

I give Huckles a large cement mixing plastic pan (found at Lowe’s) filled with shredded newspaper. She uses it as a litter box, but she digs in it all the time and nibbles the paper.

Oh, another thing I thought about for diggers is to fill a tunnel with stuff. Like one of those cat tunnel. It would be a bit like an excavation project for them and contain the mess a little. Crumpled up balls of newspaper maybe.

I agree about the dirt, it could get pretty messy indoors too. You can get washed sand for kids sandpits. I was thinking if it were damp it wouldn’t fly into the eyes and be better for digging. It can be washed and dried also. Though again, lots of work and possibly messy. And if your cats are used to sand they might start using it..
It’s tricky to come up with something the rabbits would actually take too.

I asked a vet about sand and it’s not recommended because of possible impaction and also the dirt could get in their eyes and cause irritation.

Have you tried a fleece blanket? My bunny LOVES MY blankets.. not hers. She has HER own blanket, but prefers MINE. She digs and digs, smooths it out, and binkies! Just be sure if you do, that your bunnies don’t try to ingest it.

We also tried putting blankets on the floor for Momo, and she ignores them. She prefers to dig and scoot the blankets that are in use. My husband is a weirdo and bundles up in blankets even in 100 degree weather, so there are a lot of blankets in the living room.