You could put some plant pots around it with repelling plants in: mint, rosemary, lemon basil, english lavendar. As a plus point the bunnies can eat them too!
I've also bought some citronella oil and am trying to work out the best way to use it round the aviary.
I have some little organza hangy things that I bought from here:
http://cgi.ebay.co.uk/CITRONELLA-DIFFUSERS-NATURAL-INSECT-REPELLANT-4-RABBITS-/160589213579?pt=UK_Pet_Supplies_Small_Animals&hash=item2563dcef8b
I just re-fresh them with a few drops of new oil every so often.