White vinegar is a main-stay in cleaning a rabbit's environment, but I don't think it would remove urine stains. I don't know if baking soda would work, either. I just did an internet search of "baking soda rabbit" & found they really shouldn't ingest much & I don't think it would clean anything unless damp baking soda were left on the fur for some time. How to accomplish that without the rabbit trying to lick it off is a problem. Maybe if you used a cone would do it & even then I don't think it would remove a stain. [It's great for removing baked-on spills in an oven, though.] Lemon juice has mild bleaching properties, so that might help a little.