She's chewed through a metal collar and tags. She's had surgery to deal with the damage to her mouth. We've resorted to taking off her collars, and have tried to be good about placing a leash out of sight. The process of taking off and putting on her collar is a problem because she hates it, and time consuming when she needs to go to the bathroom right now. This is on top of the table surfing she does (which is actually quite amazing considering how high she can jump). We're just frustrated, she loves and is great with our kids, and really affectionate with us, but we are just hopeful that we can find some measure of making this better.
Their is a round Nylon Choke collar that is made. You might find it on ebay. As long as it fits your dogs neck pretty close it should not hang down where your dog should be able to chew it. Another suggestion for walks might be a Gentle leader or something along that line. I have no idea if your dog pulls or not when walking but its a different kind of collar.
As far as chewing the leash goes, Tanza once suggested using Tea Tree oil to keep my dog from licking his stitch area after he was neutered. You could try putting that on the leash closest to the area where your dog could chew, treat the whole leash in bitter Apple that you can buy at Pet Smart, or try something like Vapor Rub until you find either a taste or scent that your dog does not like. Tanza was quick to tell me that Tea tree oil does not work for all dogs but it has been very effective with ours.
Hope this helps.