How can I protect my ac unit from being bumped with mower?

My neighbor is an idiot. He has come way too close to backing into my ac unit. I thought about using cinder blocks (holes on the side for airflow) with rebar behind them in case he bumps into the cinderblocks. I would really like to put barbed wire outside the cinderblocks or an electric fence but I guess that would not be very neighborly. (grin)