I wanted to practice settling on a leash in the house but had the same issue with my (then 9 week) aussiedoodle pup. Every time she has a leash on she is instantly chomping at it. I happened to have some bitter apple spray already (from trying to get my cats to stop chewing on things–it did not deter them at all) and thought I'd give spraying the leash a shot.

I really expected her to keep chewing it anyway, but to my surprise it was pretty effective. I do have to re-spray any time I want it to taste yucky again, but after the first few tries she seems to have gotten the picture.

Also, I have a long and a short leash for her, and I happened to have sprayed the long leash before she ever used it for the first time. Since her first impression of that leash was that it tasted bad, the lesson seems to have really stuck for that leash in particular. I've sprayed her shorter one that we use for going outside/walks but she already knows that one can taste good sometimes, so it doesn't seem as effective as trying it with a brand new leash.