In the words of Josh Thompson, "Our houses are protected by the Good Lord and a gun and you might meet 'em both if you show up here not welcome son..."
Lock the coop! Put up the hot wire and charge it up on the highest setting. If you're not prepared to shoot them, I'd advise firing a shot above their heads to get the point across. But, I say shoot them. However, I'd probably use my son's pellet gun or a something non-lethal. It's true, a chicken's life isn't worth carrying around the weight of killing someone for the rest of your life. If you just put up a bunch of road blocks, they'll realize it's not worth the time and move on to an easier target. How about some motion sensing lights? They are at Home Depot for under $20. Lots of lock. Alarms. Dogs.