For toothy critters in Fresh or Saltwater I use a shock tippet of wire or heavy fluro rather than a full leader. These are usually about 12 inches long and attached to a bimini twist in the the 'class tippet' via a huffnagle or albright knot. I attach the shock tippet to the fly with a no-slip loop knot.
For a great reference on knots and rigging leaders check out Practical Fishing Knots by Mark Sosin and Lefty Kreh.
Fluro does seem to vary quite a bit. I've used sci-anglers brand for most of these applications. For regular tippet material up to 20lb I like the stuff Rio puts out.
When sight fishing, look over your shoulder from time to time, you never know who's behind you