I love the idea of taking them to the pound. Nothing hurts people more than when you hit them in the wallet. I've seen even the most high and mighty dog owners learn to keep their dogs in after they've had to pay a couple hundred to get their dog out.
However, if that's not an option and you don't have a bb or paintball gun, do you own a 12 gauge shotgun? You can order bean bag bullets (NOT rubber bullets) from a sporting goods store. They are shot from the gun at a fairly close range and will really thump the dog without killing it. We use it on brown bears here and it's enough to scare them off. Just be sure not to hit them in the head or at point blank. And make absolutely sure you get bean bags, not rubber bullets. The rubber bullets have been known to kill bears, so they'd do a dog in in no time.
Best of luck. I understand the dilema you're in.