Thank you to everyone who responded.
The Garmin Rino certainly stands out as the unit of choice. You have all made it easy for me to make a decision and it seems that it will be 2 of these units. We normally carry a small GME hand-held UHF radio so as the Rino has a UHF radio function it will take this place. It basically means that we are not adding any extra weight but have so many more tracking, communication and potentially lifesaving functions. Thank you again.
Thanks for your reply Fred (FredMason) you nailed it in your description in describing just how easy it is to get lost in the harsh Western Australian bush. I note that when my wife and I are working we each concentrate on the ground and do not realise that we are wandering further apart. Suddenly you look up and realise that you can't see your partner and you are confused as to what direction you last saw her. Without a communication link this could potentially get very serious. Luckily till now the UHF radios have sorted this out and we would find each other. I am concerned that one day we will walk too far or worse, one of us will fall down a hidden mineshaft, lose conciousness and will almost be impossible to find. The Garmin Rino should be a lifesaver.
Peter.