Simple way to lock it is to use JBWeld inside the diffs. Very thick oil (200k-500k) can almost lock it, but still slips.
Not really like a slipper clutch, although the effect is similar. With a CD, it starts to wheelie and when the front gets lighter, power gets routed to the front tires. This reduces the power to the rear tires and the front doesn't go any higher. If you are really giving it a lot of power, this results in worn front tires, not to mention a lot of front tire ballooning. All this keeps more of the tires on the ground and offers better control on a track. Wheelies are impressive, but does get a little old when you aren't trying to do so.
On a track (bashing) I rely on the surface to provide slip.
