I've always bought Nepco aspen chips for Scone's litter box. Aspen's safe for rabbits, and the Nepco product has been pretty good over the years, with small, soft chips. Two weeks ago I bought a new bag, and it turned out to be large, rough chips, about an inch square and thick, and neither soft nor absorbent. Having nothing else on hand, I changed out Scone's cage and litter box with the new material.
He hated it. Worse, he refused to use the litter box at all with the new material, and started going in front of the box instead of in it. For a bunny who has always had near-perfect litter habits, this was a big change.
I found some Kaytee aspen product which looked better, and it turned out to be the small soft chips I'd been used to getting from Nepco. Unfortunately, even though I put the new chips in the litter box, Scone had gotten into the habit of using the floor in front of the box, and I spent a week cleaning up after him every time he sat near the box. I never had to litter train Scone - he used his cage from the day he was first allowed out - so I wasn't sure just how to do it now.
I started by encouraging Scone to go in the box every time I saw him near it. I'd tell him "go in the box", and eventually he would hop in and nibble on the hay. I would then praise him extravagantly, telling him what a good boy he was to go in his litter box. Within two days, he was right back where he'd always been - have a little snack on his plate, then run to the litter box and jump in. Not a single poop out of place.
I'm proud of my bunny.