Pitchforks.. shot guns in the air.. stampede him back across the owner's property and cause damage....
Keep running the bull, a good dog can run a bull...
Stampede YOUR cows across his property and cause damage...
If he is going to allow his bull on your property... go put your cows on HIS...
I think having a secondary line of defense such as Hi tension barbwire, 2-3 lines, 1 being hot, 5 feet or so inside your pasture, creating a buffer zone between his side and your side of the pasture.
If he goes through that, you have gone above the call of duty and need to call the sherriff and...