My 7 rabbits all use the patio for scent marking, as they can smell each other's 'deposits' there - it's a giant toilet :roll:
However in their living accomodation they are litter trained very very well, although some poops get kicked out of the tray when they jump out. None of the girls are spayed, all were aged about one or 2 when I got them and had never used a tray before - they took to it straight away as the trays are big, underbed boxes, with higher sides than cat litter trays, and all their hay is served in their trays, at one end of the tray so it doesn't tend to get dirty till they've sifted through it all. The 4 girls in the shed eat every bit of hay if the tray is clean - they seem to sit on it the more dirty the tray gets for some reason.
The main problem I've had is them digging up their litter trays when they get hormonal, which makes a right mess for a few days :roll: