What factors impact successful litterbox training?

Most important factor for success is having your rabbit spayed/neutered. This will reduce or eliminate their hormonal urge to mark their territory. Also, older rabbits are easier to train than younger rabbits. Young rabbits do not have the control and ability to learn that develops from age. If you have a rabbit less than 6 months, be patient & persistent. Older rabbits will usually learn in a matter of a few weeks.