I'm going to use the GPS but unfortunately today there is a really nasty east wind blowing and the temperature had gone down to -3 by early evening, so very sensibly the horses are all in the barn, sheltered from the wind and eating a new bale of haylage :-)
I know from experience that a strong wind seems to be one of the things that the horses really dislike contending with. Cold, still weather, or even wet weather doesn't drive them inside and out of the way as fast as the wind, even when its not accompanied by rain. As soon as it drops, though, I will be lashing the Garmin to Felix (as being the horse least likely to break it - it wouldn't last 5 minutes on Charlie, Jacko or Angel!) and we'll see what it shows.