The Toyota electric locker was an easy choice for me. I could pick one up for $400 used from a junkyard and make the controller for a few bucks. If the power is lost on the elocker, it will still be locked, and can be manually unlocked at any time.
In order to install the elocker, several modifications have to be made to the axle housing. These modifications are explained in great detail on several other websites, so I'm not going to go into great detail. Read these web pages and then continue reading this.