My puppy won't stop biting her leash!

Okay.  By now you have your puppy NOT biting at her leash, at least most of the time.  If your puppy is able to ignore the leash some of the time, but still insists on trying to keep biting it and won't stop when you say eh-eh and take it out of her mouth, remember, she isn't trying to be bad.  She may just be getting bored or overwhelmed and looking for a diversion. To combat this you may want to try to replace the leash with something more appropriate to chew immediately after you remove the leash from her mouth.  This can be an 'easy to carry' chew toy or stuffed toy, but shouldn't be anything edible (including pig's ears or rawhide chew bones) or something hard for the puppy to control (like a ball).  Those things tend to distract the puppy too much from the task at hand.

I like to use a length of ordinary clothesline rope.  I make it long enough so it is at least 1 to 2 times my height. I also make sure that this rope is cotton (or polyester) not treated with any chemicals, and wash it with soap and bleach then fully dry it before I use it with my puppies.  Once the rope is ready to use, I put a large knot at the end of the rope and then create several interlocking slip knots, pulling the lose end through the last loop.  If the puppy is small, I make sure these slip knots are very tight so she can't catch her head in any of the loops.  I put a knot (or knots) on the other end as well so the rope won't easily slip out of my hand if the dog grabs and runs with it, but generally hold this rope trainer near its middle.

I use this rope for several different things when I train my puppies, but with regard to leash training, I use the slip-knotted end as a diversion if the puppy insists on chewing her leash.  When she starts chewing on her leash, I say "eh-eh" (or "no" if the puppy has been trained to respond to "no") and take the leash out of her mouth, replacing it with the rope end.  After repeating this a few times, instead of actually reaching down and taking the leash out of her mouth, I say the "eh-eh" command to stop and then drag the knotted rope end past the puppy slowly, giving it a few shakes while it goes by.

Most puppies will drop the leash and go after the rope.  After I let her play with the rope for a few seconds, I pull it up out of her reach and go back to leash training.  This has worked for me with all kinds of different dogs.  Whether the puppy is an Australian Shepherd, Australian Cattle Dog, Poodle mix, Terrier, Catahoula Leopard Dog, Chow chow or Chihuahua, my rope distraction usually works for me when the puppy has trouble not biting her leash.   However, to make this work you must remember the following:

• You have to be consistent 100% of the time when your puppy attempts to bite her leash. If you only stop her on occasion, she will take much, much longer to stop this behavior.
• If you use the clothesline method for distraction, you can never yank at the rope once it is in the puppy's mouth.  You can injure the puppy and pull out some teeth.  Once the puppy latches onto the rope, put absolutely no pressure on it (but don't let her get the rope so far into her mouth that she could swallow it!)  Let her play with it and carry it in her mouth until she drops it to follow you when you move.
• DO NOT let your puppy get the rope so far into her mouth that it can be a choking hazard.  The bigger the puppy, the bigger the rope and knots you should use.  
• Never let your puppy play with the clothesline at any time if you are not connected to the other end and controlling it every second she is in contact with it.      

And although I have had this work in many cases, making short work of leash biting behavior, there are always exceptions.  One puppy I had who was a hound mix never would chase the rope.  She never even showed any interest in it.  To get her to stop biting at her leash, I started with her fetching a ball for very short distances in a closed space without a leash on her.  I rolled the ball further and further and had her bring it back to me each time (this was easy because we were in a space the size of a closet).  As she got more engrossed in this game, I attached her leash to her collar and continued the game.  After a few sessions like this, this puppy stopped biting the leash when I put it on her and paid more attention to whatever we were going to do.