If the dogs teeth are getting caught I'd use cow-hide like Holly stated. Here's a link if you're interested in ordering some. Stillwater Kennel Supply --
I am currently using bunge cord that I bought off a friend, it works great has spring and is durable, not to mention my dogs can't really hurt their teeth on hitting a metal spring.
Being a pitbull owner isn't a right, it's a privilege! The ability to own one doesn't make you a pitbull owner, it's how you take on the role of being a responsible pitbull owner that makes you a pitbull owner.