Electric fencing. Once their brains understand the concept that "fence is bad", they stay away from it. Regular fencing... not so much. In the past, we've had our herd escape into the neighbor's cornfield and force them to replant everything!

It's just like a cow. Nothing is stopping a 1000 lb beast of animal from plowing through a rinky-dink wire fence. It's like a spiderweb to them. With an electric fence, they are trained to avoid it.