erm, incontinence can be to do with legs!
I'm not a vet, but my experience in humans leads me to suggest one of the following:
spinal tumour
spinal infection
spinal fracture
I doubt whether any of these could realistically be treated in a rabbit, sorry
Lisalisa, could you come round to the idea of a funeral for the rabbit? I would imagine it would help ds to be able to say goodbye properly, say a prayer over the grave, plant a flower, or paint a nice stone to mark the grave. It could also help him to deal with (God forbid) and human deaths he encounters in the future, if he knows roughly what happens...