wolf urine...
they sell it by the bottle at sites like this:
http://www.predatorpee.com/
it should keep larger animals away....
you can also try setting up some trip wires, attached to party poppers like this:
http://en.wikipedia.org/wiki/Party_popper
if not, then just trip wires hooked up to a big bell... the clank should startle the animal enough that they stay away...
if it's a rabbit it may dig below the chicken wire.... so bury it a foot under the ground....
have you noticed a little tunnel, hole, or any entry point??