I recommend not allowing him on the bed. A big part of litterbox adherence is being neutered, as the hormonally-driven urge to mark territory is drastically reduced. That being said, even among spayed/neutered rabbits, the bed is a very common place for rabbits to mark. It is soft and is full of scents to mark over and claim, and rabbits love marking that type of stuff!
You can also have a shower curtain or some sort of cover you place over your bed to make it easier to clean/less attractive for your rabbit to hop on and mark. Since this is a very natural behavior for rabbits, I don’t recommend taking measures to “train it out” of the rabbit, as those attempts often fail with rabbit behaviors owners don’t like, like chewing and digging, haha.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.