Wat you want is the Garmin Map76. You don't have to do anything but turn it on, it starts laying down a track of bread crumbs on the basemap, and when the fog rolls in just follow the crumbs back to the boat launch. It also has all the navigation aids in the States and Canada on the basemap, so even if you have never been there you can navigate with it. This is a handheld unit, but I find it most convenient in foggy and dark conditions to stick the thing in my face, so I can look for deadheads with one eye and the route with the other, and when it clears up I just turn it off and put it in my pocket, so I never bother with a holder. You can get these for under $300 delivered if you look around on the net.