Man, you must live in a really wild area! I think I would get a 22 filled with "scatter shot" and shoot me some horses and a bull! It won't hurt them unless you are practically sitting on them, but it will sting so bad they will remember where it came from and hopefully stay away from your yard. Certainly after the 2nd or 3rd time!! Just thinking.... Maybe a bull dog like mine would scare the bull or horses away? He'd surely try. That fool is lucky you don't eat that bull of his. What are the laws on things like that? You should be able to sue him for damage to fences, gardens, etc. : )
I have 5 dogs- 4 here and one on the road. I'll write it up at some point because it's ongoing and convoluted. .....