For mysterious reasons, I can't post an answer to your blog, it accuses me in red print of making mysterious errors but doesn't specify their nature. Very Kafkaesque,

Hey, he really is cute, for a possum.

If you garden, a possum is your friend. Eats snails! Yes, snails, and slugs, too. Maybe even puppy dogs' tails, and whatever else little boys are made of. Also eats insects. But as you just discovered, if you leave cat food outside, he likes that even better. He's a carnivorous-leaning omnivore, like us, but with a special French tastes for les escargots cru.

One thing you don't want to do is scare him into "playing possum," where he'll pretend to be dead and secrete some stinky exudate that will make him smell not just dead, but dead for about a week in hot weather. Yuck!

In the South, they are occasionally roasted with sweet potatoes. At a great butcher shop in the Fillmore District (before the neighborhood was gentrified) they offered possum around Xmas, always with the feet still on to demonstrate definitively it was real possum, not Fluffy the Cat.

So, two alternatives. One: live with him and let him clear your garden of snails and slugs, and don't terrify him. Two: call local animal control to move him somewhere. Three (that's three possibilities of two), keep your cat food inside, and let him eat snails. And hope he's not a she, which might eventually bring a possum explosion.