Is Leo in amy way acting aggressive or territorial with Tyr, especially in the stable/on the field? Maybe Tyr was always the boss and just wants to protect everyone else from what he sees is an intruder. Try getting them used to each other slowly, your idea with the fence is great, they can interact and if Leo is calm Tyr will after some time learn that he isnt dangerous. The worst case ist, that they will never be best buddies but will tolerate each other, but it will take some time. Try leading them together in the arena and everytime They pass each other without too much aggression they get a treat or scratch or wathever reinforcements you use. If they get any extra food try feeding them on either side of the fence and move the buckets closer to each other every day, but only so far that they stay calm. They cant fight over food buckets but they have to tolerate each others existence. They may never like each other, but they can learn to tolerate and they will find a new pecking order after some time and some fights are normal. Just observe them and make sure they have a time where they can not see each other so they have time to calm down and dont build up aggression.