The only stallion I knew before was a tb hunter who was perfectly behaved unless in his box, I can remember picking his feet out and having riding lessons on him at the age of about 8, but only my aunt (his groom) and his owner were safe to go in his box because he was so territorial.
Corsario was puzzled at first when I started my campaign, apparently all the biting started after he went away for a year to be backed, before that he was sweet-natured. We think he must of been hit a lot while he was there for normal mouthing behaviour, because he tries to get a lightning-fast bite then move away. Waiting until he softens his eye and puts his head down has taken about 4 months to really take effect on him. Yesterday he was gently mouthing my open hand without trying to bite at all which felt like a real step forwards.
I've never shouted at or threatened him in any way so he should get the mesage in the end.
Needless to say, Rudi is not going away to be backed, nor will any of the other horses.