I would say you have your work cut out trying to nip that habbit in the bud...and like stated they could be far worse bad habbit's out there...if possible can you not get the dog in among good number's of bunnies..i had a dog a while back that would start the night pretty hard hard mouthed when he was keen and fresh...but as the night went on he would settle down and not smash them up so bad..
On the barbed wire..you could give razor barb ago as that is sharp as fook..