It depends how permanent you want it.
I'm a huge fan of a product called Fiber Fix. It's a "tape" that you wet and wrap that sets up harder than a cast. Its supposedly tough enough to "mend" a broken shovel handle or repair a burst water pipe.
I use it to wrap all of my tomahawk and axe handles. Some I wrap completely because the Fiber Fix sets up with a really rough skate board tape like finish. Some I only wrap under the head to protect the haft from over strikes.
The one thing to keep in mind is that Fiber Fix is one and done. You open the whole wrap, you use the whole wrap, and there is no saving any of it. The good news, it's cheap. Less than $10 at most big box home improvement stores like Lowes.
It is very permanent though. The epoxy is very strong and the fibrous material is tough as can be. Once it's on, I dunno how you can realistically get it off. I figure for the cheap hawks it protects now, if I ever manage to crack the handle, I'll just burn the whole thing out of the eye.