I agree on MUD. However, a lot of rivers I fish have sand. I bought a little tin of MUD from Orvis. Worked great. Got the fly down then washed off as it floated. But it also took the shine off thee tippet or leader.
Only need a little bit. Here is some from Loon
http://www.amazon.com/Loon-Outdoors-.../dp/B002XJTN5Y