Clipping wings will not always stop them from flying over fences or into trees. And as Drumstick Diva has mentioned, wings are their only defense against predators....they can fly away. So I really don't recommend any clipping. The better thing to do is keep a good rooster and keep an eye on your flock. When you free range you take your chances with loosing birds.
Don't clip ok it's like the outside cat that gets declawed. The only reason you clips is if there flying over the fence yard there in but still you only do one wing. If you do two they can still fly some .