Mr Milan Janus, the Czech famous competitive fly fisherman, developed his own version of French leader for light nymphing. The leader consists of 8 metres long mono section made out of heavy Blue Fluor tippet (which is easy to cast, high visible for the flyfisherman and almost invisible for the fish) and short hi-visible spiral indicator. This leader works perfect with long 2-3wt rod of medium action - like Marryat 10ft 3wt when fishing with light nymphs up stream or fishing Czech nymph style. 

The French competition fly fishers are well known for fishing with very long leaders. This technique is incredibly effective in smaller, shallow and clean rivers. It enables perfect casts even the smallest flies.