I know someone in WI that was prosecuted for shooting a 'wild' dog. If the owner finds out, you have no legal leg to stand on unless it's an act of self defense.

You're better off IMO calling animal control and/or trapping them. It's fairly easy to trap most dogs in a live trap. Plus, it's more ethical. If the dogs have collars, it's someone's dog...that means it's not a matter of bad dogs, but rather, bad owners. I've trapped a few dogs and turned them over to animal control (humane society). It's the best solution for everyone IMO...the dogs are rid of the bad owner and get adopted by someone more responsible, and you're rid of the dog.

It they're truly wild and rapid, that's a different story, as they're actually a danger to people. Most 'wild' dogs, in my experience, aren't wild, but just strays that crappy owners let run loose.