My purpose in posting this is to let you know that it is possible for chickens and possums to coexist without loss, and in no way do I want to debate the issue, but rather to tell you what has worked for me, just so you know there are options.
Possums are opportunist, they are looking for the easiest meal they can get.
Here they come up and eat cat food we leave out on the porch for the cats, they visit my porch instead of bothering my chickens, they stay happy and healthy, and even keep a cleaner coat.
I will catch them bare handed sometimes just to remind them that they aren't the biggest predator here.
They are wild, and after I catch them it takes a week or two before they get brave enough to come back.
I understand that this won't work for everyone, and I'm not sugguesting that you go out and catch a possum this way, and we all do what we feel we need to do to protect our birds, I have no problem with that and if I were to find a possum trying to get into my coops I'm quite sure it would be dispatched, but if your coops and runs are as secure as they should be then you'll find that you don't have to kill every single predator you see.
We have all kinds of predators here including possums, coons, coyote, hawks, owls and feral cats & dogs.
To date I have never lost a bird to any predator, and have owned chickens for over 2 years now.