Your Garmin help, please

I just plot the route as a GPX and display it on the map as a light blue line.

Ride with the GPS on the map page and make sure you're not off the blue line. Also stops me looking at the numbers page which only leads to madness.

The Edge 705 can be made to do routing well as you can upload a route (with the GPXX extensions) with thousands+ of points in it so the GPS has no option but to send you exactly the way you want as there's never any choice of the route between points that are 10 or 20 yards apart. Initial route calculations take ages though, which is a pain.

I have the route as a GPX track. I load it on the Garmin 800. The Garmin then decides it's not happy with my route and fucks it up, so the map uses some other roads. I presume you're using an etrex or something that doesn't do turn-by-turn? Is there a way to stop the 800 doing turn by turn if it fucks up the carefully planned route I've created?