I think spraying some pyrethrum on your plants might work. We have the same pesky possum problem. They eat the oak tree out front on nature strip. I parked my car out there the other night, and they must have been having one hell of a party on top of it... munching acorns, piddling etc... grrr!
Anyway, they are also eating my petunia flowers, so I sprayed the pyretrum on them, and it seems to work. I don't want to feed them either, attracts more rats.
Incidentally, our little manx cat caught her first humungous rat the other night.
