Was looking up for solution on rabbit urine odor and found “The best thing that I have used so far is 3 table spoons of baking soda in the drop trey or litter box to help with the odor“.
I will be trying this out very soon although I do not have a problem with how my bunnies smell at the moment.
Generally, this is one of my favourite sites:
Tru-Luv Rabbitry: Quality Holland Lops in Malaysia 