Awwww, come on y'all. Possumproof your pens, then live and let live. It's not too hard because they're not very bright.
I can understand the rage when you catch something killing your girls. I nearly killed a dog that I caught tearing my cat apart. He got away and never came back, but he would have been dead if he'd stayed.
But possums aren't as fierce as they look. It's just their job to be as ugly as they can because that's almost all the defense they've got. (me, too.)
And they're really interesting, if you read up on them. They've been around a long time, even though their natural life span is only three years. They're blind in the average daylight. They don't tend to get rabies. The biologists think it's either because 1)their body temperature is too low to support the rabies virus or 2)their nervous system is too primitive to support the virus.
I've rescued and raised the babies, and they're fun to watch, even if they aren't that outgoing.