With the idea of getting frantic action from flies, a group of west coast anglers have been experimenting for a few years with rear weighting flies. When balanced properly, which takes some trial and error, such adapted flies will dart very erratically when retrieved.

For several of the adapted patterns, the key to the weighting is to add the weight past the bend of the hook. This is usually accomplished by tying a length of very heavy mono (80lb test or so) to the hook shank so that it extends beyond the bend. Lead wire is wrapped around the mono and secured in place. The pattern is then tied normally. Dan Blanton wrote an article for Fly Fishing in Saltwaters that demonstrated this adaptation for the Sar-Mul-Mac. Other patterns have been adapted as well and at least one original pattern developed as shown here: www.danblanton.com/SSTstory.html

The result is quite unlike any other fly behavior I have ever seen.