When off-road, the absolute best available traction device available comes in the form of a spool. There is nothing that is stronger, lighter, cheaper, or runs cooler. In fact, a spool is not really even a differential, as there is no differentiation of wheel speeds with a spool. The lack of wheel-speed differentiation in a fixed-gear unit (i.e. a spool) is the very thing that makes it horrific to deal with on the pavement. Differentials were invented to allow for different wheel speeds when not moving in a straightforward direction (as in turning).
If you've got a somewhat serious but still street-legal off-road vehicle, there is only one way to go: a selectable locker. A selectable locker allows you to differentiate in between an open-differential mode and a 100 percent locked-together spool mode.
One of our favorite selectable lockers has to be the Ox Locker. The Ox is crafted from 8620 steel and has a locking gear and ring that engage an overbuilt differential locking system, all with the pull of a cable. The cable is one of our favorite features because as long as you can pull on the cable, you can always engage it. Electric actuation and air actuation are very good ways to engage a locker as well, and we've had lots of success with both, but both can be potentially left vulnerable to electrical or air-line failure. With a cable actuation, we could still get our rearend locked even if the battery had fallen out, our air supply was gone, and the truck was under water ... not that we'd still be trying to drive it in this state.
We've actually used an Ox Locker before, and it worked just as well in our rear Dana 60 as it did the first time we tried one. Locking the rear up with the locker shifter truly creates a spooled rearend with absolutely no differentiation in tire speed. Unfortunately, we haven't gotten to put too many miles on this diff, but the miles we have put on were fun ones. Everything seems to be working well. We forget it is in the back of the truck until we need it, and that's just the way it's supposed to be. One complaint we have heard is that the cables stretch over time after multiple uses. There is some adjustment in the cable, so we doubt you'll get to the point where you'll have to buy another cable housing to replace your old one. Should you need to buy another one, a variety of lengths are available.
At the time of writing, Ox now has an air-actuating locking mechanism available for the Ox Locker, should you choose to run an air line instead of a cable. Ox is also working on an electric actuator to bolt onto the cover.