One of the things that makes bunnies such good house pets is that they are very easy to litter train. Once they have settled in to a new home, they will generally settle on a particular corner and into that corner you put the litter tray and the job is done. They are clean and tidy creatures, so once the toilet area is established they will stick to it and your nice carpets (and sofa) will be safe.
Having established this, you can also move the litter tray. This is especially useful if the corner they picked wasn't the one that you wanted them to use (why do they always pick the one by the door?). If you do this gradually, the bunnies will return to the same spot each time, see (well, probably smell) the tray and use it. Any, er, misunderstandings can be moved into the tray and they will soon get the idea.
Moving the tray quickly to another corner is asking for trouble. The bunnies will return to the original corner, finding no tray will just assume you have cleaned up for them and start again (just like if you'd put a clean tray back). Not only that, but when they find the tray elsewhere they'll take that as you green-lighting an additional toilet area and now you have two. This very thing has happened to me when I have placed a soiled tray down somewhere while I replace it and turned my back for a moment only to find a bunny using it. Then the next day, guess what? New pile of poo in that spot. Be warned. Anyway..
There is something I would like to touch on here, another word of warning really. The religious using of the litter tray without accident can be quickly disrupted if you do anything to disturb their routine or incur their wrath. If, for example, you were to bring home some temporary foster bunnies and let them play in your (their) garden you will quickly discover that your bunnies will make you pay for this crime by giving to you the gift of an afternoon of picking their poo out of the grass. From across the whole lawn. The books will tell you this is a territorial thing as they try to claim back their space from the interlopers, but I tell you now, I've seen revenge in their eyes as they glare back at me... Moving on.
Now, the reason I mention all this today is that Santa and Jemima have recently altered their own morning routine. Rather than hopping back into their fresh litter trays for their big post-breakfast clearout, they've found a new spot.