We've had this problem with our 8 yr old guarding food from 4 older males. 2 are gelded, outside I thought it was just boys since it doesn't happen all the time. Well he won't let them in the shed I had the hay in there since its colder blowing snow etc here in Iowa. So I put him alone in his own pen when someone would even look in the door he would stick his head through the rails growl and spit at them.. I put his buddy in with him , didn't help. He guarded him from his fool as well. Today he has started to rear up on the pen. So I thought let him out and watch him, maybe I'm making him more frustrated and mad. So he was out and I was watching him and he did it again to the boys who just eating by themselves. So got him back in pen and then he nibbled on my hat. Now I'm wondering what to do with this situation. I'm retired now so I'm home. If he's out with the others he guards hay which is outside all day I have 4 different places to eat from. So they do eat outside till he comes to their feeding area them he growls and chases them sometimes . This has started in the last year I guess, It's just gotten worse..Sorry for rambling on. I get 3 females in 2 weeks. These 5 boys have been really good for the most part. We now have snow so no pasture to get away from each other. I'm not sure what to do, I'm not used to aggressive behavior till now.