A diff guard should be fitted to the front and rear diffs. Both of these diffs are venerable to damage or worse from rocks and stumps hidden in long grass, river beds etc.  The front and rear diff housings are quite strong but the banjo is only a tin cover easily dented and sometimes pierced. All it takes is a stump or rock not seen by the driver as it maybe covered or hidden by grass or even under water to be driven into. The tin plate will get dented forced against the crown wheel and be opened like a tin can. If this happens the vehicle will have to be repaired straight away as it will no longer be able to hold in the oil, but even worse if unnoticed major damage will happen to the diff requiring replacement.

Diff guards are not new to the 4WD industry. Some guards are fixed by clamping around the weak tin banjo, which is easy to fit but on impact only relies on the strength of the actual tin for protection. These guards can also be lost if the guard is dragged away from the diff housing (common on rear diffs). Some other methods of attaching will not allow the diff guard to be fitted to the rear diff housing.