You need to train him.
Pure and simple. A leash is the best place to start. There won't be any question as to what you expect. Reward good behavoir. On lead ask him to pay attention to you and reward. If a cat comes within eye contact reward him for paying attention to you. When he looks away get his attention and reward. You will have to put in the time. When he is not on lead with you training, he needs to be kept away from the barnyard.
Good Luck-it can be done.
Pure and simple. A leash is the best place to start. There won't be any question as to what you expect. Reward good behavoir. On lead ask him to pay attention to you and reward. If a cat comes within eye contact reward him for paying attention to you. When he looks away get his attention and reward. You will have to put in the time. When he is not on lead with you training, he needs to be kept away from the barnyard.
Good Luck-it can be done.