Isn’t there a device that is used to control bulls by surrounding them with a round metal fence that isn’t anchored to the ground? The idea is that the bull can’t run and can’t get to the cows, etc., but he can still graze and can shove the ring around to move as needed.
I could swear I’ve seen these things but I recently asked my uncle, who has owned a few bulls in his day, and he had no idea what I’m talking about. Googling for bullpen, bull ring, etc. only gets me baseball and bullfighting references.
The thing I’m thinking of is about 20 feet in diameter, maybe five feet tall, and made of tubular metal.