I would call the police and file a report and also let them know that there are squatters in that barn that are growing and selling drugs. The idea of waiting in the coop with a shotgun sounds good. I had some local gang bangers try to break into my car one night and after I came out of the house with my .45 I haven't had any problems since. But that said, people growing and selling drugs are highly unpredictable, you should definitely start with the police first, shooting an unarmed person (even if they are on your property) can bring you alot of grief and possibly jail time. Some counties have laws that state you are not allowed to defend yourself with more than your attacker (yes it is stupid) but they are out there. Also, unless they are IN your home you are not allowed to shoot them unless they attack you. There was just a report in the news this week about a man that was arrested because some gangbangers came onto his property to attack him and a friend, he went inside and got a rifle and fired it into the ground when 30 of them came onto his property, he didn't even shoot at them just into the ground and the air. If you can go with game cameras (or even CCTV) that would be better and you can give the pictures or video to the police.