I recently purchased a new Oregon 600t and now have two data cables. So, I've started loading both my Oregon and my Nuvi with my cache targets of the day.
Since, my wife can't read a map, the Nuvi is great to give me turn by turn to get me to a parking spot. Once parked, I use my Oregon and my wife uses her iphone.
If I log the find instead of my wife I use my iphone. Since I started this process, the fights have gone way down.