Around here we can borrow large trap-cages from the local pound for feral cats. A tempting bait is put inside, the cat goes in, and the wire door slams behind it. The city pound then picks up the cat in the cage, and if it has a tag the owners are notified. It costs $48.50 to retrieve your pet from the pound. The animals aren't hurt, and the owners pay to learn their lesson.
Around here the coyotes take care of the feral (and domestic) cat problem.