I had APT differential guards on my Discovery 2. I was very impressed by the build quality and fit of those guards and so it not a hard decisions to fit them to the Defender.  

I bought my differential guards from Peter and Nick at PCB Land Rover in Adelaide. I like PCB Land Rover as everyone there is very knowledgeable about the vehicles and are extremely friendly and helpful. I think they are the distributor for APT products within South Australia.

The rear guard is very similar to the one that went onto the Discovery 2.