Cortland Toothy Critter Tie-Able Wire Leader
Aptly named, Toothy Critter is tough as steel (because it is) a leader material that is supple enough for tying all common fly fishing leader knots. It is tough enough to stand up to the sharpest teeth.
Another redeeming quality of Toothy Critter is its near invisibility in the water. This material is about the same diameter as monofilament, so it doesn't effect casting or presentation. If you fish for species with teeth, you will like Toothy Critter.