A former Marine Scout Sniper has a new book out. It's called Index Tracking: Essential Guide to Trailing Man and Beast, by Freddy Osuna. I first met Freddy on a tracking course at Camp Pendleton about six years ago. Since then I've taught alongside him a couple of times and I can say this with utter certainty: he's a far better tracker than I (which might not be saying much) and many others I've seen (which is saying much). His visual acuity and off-hand ability to locate and interpret action indicators puts my best efforts to shame.
Freddy was with 1/4 as a grunt squad leader before completing the Scout Sniper indoc program and Scout Sniper school. He worked as the Staff NOCIC of the 1ST Marine Marksmanship Training Unit (which was where I met him) but was eventually medically separated for injuries sustained in OIF 2. He's one of those guys who is genuinely passionate about teaching (he was awarded a Gold Star for his Marine Corps Achievement Medal in lieu of second award for excellence in innovative training techniques). If he is as good at communicating tracking techniques in book form as he is instructing it on the ground, it's going to worth reading.
I haven't read the book yet, it's on the way. If you're interested in tracking though, whether combat tracking or visual sign interpretation from basic infantry operations to Combat Hunter to law enforcement work, it's a pretty safe bet this will be a good addition to your library.
In the meantime here is a review from Amazon by Troy Lettieri, whose opinion on the matter can be trusted: "The book "Index Tracking: Essential Guide to Trailing Man and Beast" is a new addition to tracking realm by Freddy Osuna. The author is Native American Yaqui Indian, former USMC Scout-Sniper who was honorably retired in 2008. Following his military career he was a tracking instructor for Tactical Tracking Operations School (TTOS) (founded by David Scott-Donelan) at the U.S. Army Combat Tracking School, Fort Huachuca, Arizona [Note: and went on to instruct for the Scott-Donelan Tracking School]. With this varied background and heritage Osuna brings an enlightening perspective on this art and science. With this book he provides a very good introduction to the fundamentals of visual tracking culminating into the last section of the book that covers Osuna's Index Tracking method which is essentially singleton based tactics and techniques for visual tracking. Other highlights in this book for me were the sections on; the Trackers OODA Loop, Aging; covering the Greenside Training basic elements and Ground Sign Interpretation. Additionally for a compact book at almost 100 pages it is densely packed with a lot of information. As well this book is profusely illustrated with color diagrams and photography that provided added depth to the book. Overall this is a respectable title to add to your professional tracking library, whether you track animals or humans or track for recreation or combat."