The corner is the rabbit's decision, not yours
Rabbits pick a toilet the way they pick everything: by territory, smell and routine. A corner behind a sofa is a classic choice — enclosed on two sides, overlooked by the room, on the route the rabbit already patrols. Owners who fight the choice and place a beautiful box in a sensible spot usually get a rabbit who toilets beside the box, in the original corner, with great consistency. So surrender early and build the system where he has voted for it. The whole arrangement that follows assumes the box lives behind the sofa, and that this is a design feature rather than a defeat.
If the corner is genuinely unreachable — sofa flat to the wall, rabbit squeezing down a gap you cannot clean — then block that gap and offer the nearest reachable corner on the same wall as the compromise, with a second box there during the changeover. But if you can reach it, keep it.
Box, litter and the hay that seals the deal
Behind-sofa space is usually long and low, so think in trays rather than tall corner boxes. A large cat litter tray with one low side, or a shallow under-bed storage box, slides into the gap and gives an adult rabbit room to turn around, which a cramped tray does not. Pull the sofa a few centimetres forward from the wall if you can; those centimetres are the difference between a box you can slide out to clean and one that festers because cleaning it means moving furniture.
Line the tray with paper-based litter or plain compressed wood pellets sold as stove fuel, both absorbent, low-dust and safe around an animal who will nibble his surroundings. Keep clay and clumping cat litters out entirely — a rabbit who ingests clumping litter while grooming or grazing is a vet visit waiting to happen. Then add the ingredient that actually trains the system: a fat handful of hay heaped at one end of the box, refreshed daily. Rabbits graze and toilet at the same time, so a box with hay in it reads as a dining spot with benefits, and a hay rack hung just above the box achieves the same pairing.
Protecting the floor and the skirting
Urine is the enemy of the floor behind a sofa, not of the system, so protect before the first accident soaks through. A washable waterproof mat or a length of lino offcut under the tray and extending a body-length behind it catches overshoot, including the classic rabbit manoeuvre of backing into the corner and lifting over the tray's edge. A slightly larger tray, or one with a high back placed against the wall, contains most of that.
Accidents outside the box get cleaned with a plain vinegar-and-water solution and never with anything strongly scented, and any stray droppings are simply swept — dry pellets are normal rabbit output and not a training failure. If puddles keep landing in one spot just outside the tray, the rabbit is telling you the box wants to move six inches; obey him.
Keeping the household from tidying it away
The fragile part of this system is other people. To a tidier eye, a litter tray behind the sofa looks misplaced, and one well-meaning relocation to the utility room resets weeks of habit overnight. So the arrangement gets explained once, to everyone: the tray stays, the hay gets topped up daily, the mat gets washed weekly, and the sofa stays those few centimetres off the wall on purpose. Add the layout to your rabbit's KinsLe profile through Family Sharing — box position, litter type, hay routine — so a house-sitter or family member covering a weekend maintains the corner exactly as the rabbit designed it, rather than improving it into failure.