The best advice I can offer on litter-training rabbits, is to be persistent and consistent. Hazel and Saturn still leave little round 'gifts' to mark their territory and trails. Fortunatly, that's easy enough to clean up! I use a product called "Febreeze" to get rid of any smell, and to discourage repeat performances. More than anything, it's important to choose your tactic and stick with it. That helps the rabbits learn.
Choose two or three litterboxes (or more - I'm using 4 for two rabbits), make them different shapes and sizes. Try to find high-backed litter boxes. I didn't want to pay the bill for fancy boxes, so I went to a discount store nearby, and found plastic dish bins for $1 each. I bought two -- one in a dark color, one in a light color. Then, I bought two high-backed corner litter boxes at a pet store. I paid over $5 each for those. Hazel and Saturn spend most of their time in their 2-floor condo, so I placed a dish bin on each floor, in opposite corners, and used the triangular boxes in the corners near the top and bottom of the ramp. Rabbits naturally head to the back corners of the cages (away from the doors) to do their business, so no matter which floor they were on, or which corner they chose, they ended up in a box of litter. After experimenting, I found my rabbits prefer the dishpans to the expensive pet store corner boxes (though they will use either, if they need to), and that they prefer dust-free clay litter to anything else I've tried. A friend of mine has a rabbit who prefers newspaper that's gone though her office shredder. He won't use the litter box unless it has 'correctly' shredded newspaper. My two are diggers (especially Hazel), so that explains their preference of clay litter. Many people (including highly-respected vets, trained in rabbit health), recommend "CareFresh" brand litter. I can't get that brand locally, so I get a dust-free, perfume-free scoopable variety. I usually add a bit of baking soda to each one. That absorbs odors, and I've found that Saturn and Hazel are less likely to taste-test litter after I've added baking soda.
Don't put the rabbits in the boxes, or put them in a position where they are forced to go into the boxes. Rabbits, like humans, respond best when they are given the time to explore and learn things at their own pace, on their own terms. Forcing them into the boxes, or changing your voice (using a stern, angry, or raised voice) for using the box improperly (for digging and playing), will teach them to avoid litterboxes. Praise them for exploring the litterbox, and for using it properly. Some rabbits will take longer to get used to the box in their territory, others will hop into them within a couple of minutes.
At first, Saturn and Hazel kept shoving the litterboxes around, dumping them over, etc. They refused to use them! I just kept putting them back in exactly the same places and filling them with litter. Also, after I cleaned up their messes, I'd put the paper towels I used to clean up in the boxes, to help them figure out what the boxes were for. It took about 5 weeks for my 2 to figure out the litterbox 'trick.' Now, the boxes can be put almost anywhere in the house, and they will hold on until they find a box of litter. They do prefer certain corners, and it occasionally backfires (try packing or unpacking boxes where 2 rabbits think every box is just for them!).
Consistency
-use the same litter boxes until the rabbits know what they're for
-keep the litter clean; rabbits don't like wet / dirty rear ends, and will avoid a dirty litter box - I have some rather amusing stories on this point ... ;)
-keep the boxes in the same positions until the rabbits are trained (they will probably move them around, keep moving them back)
-use the same litter until the rabbits are litter trained, unless the rabbit absolutely avoids the litter box, and there is reason to believe that the litter is the problem. Start with something soft, like newspaper, and don't start with something that will make the rabbit think it's food - like corn cob pellets; they make great litter, but it is nearly impossible to train a rabbit with them.
-don't say 'bad' or any other negative comment if they dig in the box or do something else. As long as they are in the box at all, they should be petted and praised.
Persistence
-It may take quite a while for your rabbits to learn to use the litter box. Some rabbits are more picky / fussy than others, and prefer different corners, colors, shapes, or heights of boxes. Rabbits have different preferences and personalities. Keep that in mind when doing training of any kind. There is no single answer. Whatever works best for you and your rabbits is the right answer for you and your rabbits!
Special Problems
I touched on these briefly, but I think they're worth a little more explaination.
Throwing Litterboxes (Saturn)
Some rabbits, despite their size, like to fling things around. This applies to litterboxes, as well! If your rabbit is in this habit, you may want to make certain that the litterbox can't be moved around. Either buy a heavy litterbox, or drill two small holes about an inch apart on either end of one of the long sides of the litterbox (use a drill or Dremel tool, or place the box on a scrap piece of wood, and use a hammer and nail to make the holes). Then you can use vinyl coated twist ties to secure the litterbox to something. Eventually, you will be able to leave the litterbox without securing it, and your rabbit won't try to move it around. Though if they jump into it, and it's on a smooth surface, like linoleum, you may want to leave the litterbox secured to something, so it won't slide!
Digging in Litter (Hazel)
If the problem is digging, you can purchase a deep container, such as a cement mixing tub (from a hardware store). You can make 'steps' with cardboard boxes (be prepared to replace them, as they will get chewed up!), or you may cut down a small area to allow easier access to the rabbit(s). If you cut the box down, be sure to smooth the edges (steel wool or sand paper work, depending on the material that the container is made out of). Don't leave sharp edges or 'splinters' of plastic.
As you and your rabbits get to know one another better, training of all kinds will be a little easier.
For more information about litter-training rabbits, please visit the "Rabbit Care Resources" page.
If you have Marinell Harriman's book, "House Rabbit Handbook" (3rd Ed.), you can find more litter training advice on pages 22-24.
