Im a Marine and I just retunred from Afghan a few months ago. I carried my Esee 4 attached to my plate carrier, and my Spyderco Millie clipped in my pocket. I also had an Esee Izula, Esee 5, Leatherman Wave, Spyderco Tenacious, and an Emerson Comander with me. Although most of those stayed packed up most of the time except for my Esee 4 and Millie. My tenacious was my lend-out knife which I ended up giving to a friend, my Millie was used for almost everything, and my Esee 4 was my hard use knife. I used it from everything to cutting blocks of c-4 to digging in the ground in search of IED's, and the edge has yet to chip anywhere. The esee 5 is a great knife, it is just too big for my needs, but it still did see some action. I was definately not afraid of breaking it. For my next fixed blade I am looking for something a little more fighting oreinted. The esee 4 would get the job done, but it isnt really designed as a fighting knife.
On another note, I just recently purchased an RMJ Tactical Shrike tomahawk, and it is an awesome piece of gear. I wish I had it with me on my last deployment.
If he appreciates knives, anything you get him he will be happy with.