We don't have possums here in Colorado, but when we lived in Indiana, heavily wooded and rural, possums were the biggest problem we had with predators. They possums seemed to become active in the early part of the night, because if we were a little late shutting the chickens into their coop, we would occasionally come into the coop in the morning to find several dead chickens and a possum peacefully sleeping in one of the nests! We probably inadvertently closed him in with the chickens. Our big aierdale was happy to remove the possum from the nest for us, and would shake it up pretty vigorously until it seemed quite dead, would lose interest eventually leave the supposed corpse in the yard. I've watched them - after a really long wait -very cautiously
raise their heads, look around, and then wander off apparently unhurt. They are amazing and really interesting to be able to observe, which isn't a common opportunity. We never had any trouble with them during the day, but had to be absolutely religious about having the chickens shut in at early nightfall.
I like the gentle approach of catfood on the porch but fear that that would also draw a host of unwelcome visitors - rats, bears, etc, depending on your area.