In my longer races, I have worn a Garmin on one wrist and a standard stop watch on the other.  I start both at the same time.  When the Garmin goes (my old 205 typically lasts a little longer than 12 hours), I ditch it and just rely on the the stop watch.

You can also rig up something like this:

http://www.runtrails.net/garmin305.html

If I really wanna know, I'll use two Garmins, swapping out at some drop bag.

(Mostly, I just do it because I think it's neat to have my course maps when I'm done.)

But, usually I don't really wanna know that badly. And, between inaccuracy of trail race mileage and inaccuracy of my Garmins, the margin for error is so high ... well, it's not worth the mental aggravation for me.

More and more, I'm running with just a running watch. (In fact, I recently bought a new one with more lap capacity for timed ultras.)

I still make "pace bands" for most races - A, B, C goals and cut-off (which might be B or C goal!).

I either tape them to my water bottle or loop them around the strap on my pack - laminated with clear packing tape.

If I'm feeling frisky, I'll mix in the course elevation profile or do it as a separate band.

I still make "pace bands" for most races - A, B, C goals and cut-off (which might be B or C goal!).

I either tape them to my water bottle or loop them around the strap on my pack - laminated with clear packing tape.

If I'm feeling frisky, I'll mix in the course elevation profile or do it as a separate band.

I have done this and the just rely on other people telling me what time it is.  I can usually catch someone at an aid station with a watch.  I put race time and actual time (expected) on my pace sheet so no matter which the aid station person yelled at me I could tell if I was on track or not.  Personally I didn't want to be a slave to an exact pace for the entire race (which I would have felt if wearing and able to know my constant pace) but liked knowing if I was ahead, close, or behind pace at each aid station.  I was able to run more by feel and had a great experience.

I have thought of capturing the entire route too.  If I were going to do that I might put the gps in my back pack or somewhere I couldn't see it.  That way it is still gathering the information for me to analyze later but I don't have to concern myself with it during the race.

I stick a handheld (GPSmap 60csx or 62sc) with lithium batteries (longer lived and works better in cold than alkaline or rechargeable) in my pack. I like to make maps. Easy to change AA if in really long races. That gets better data than the wrist-mounted ones anyway. The newer wrist-mounted ones (910xt) are supposed to have longer battery lives - about 20 hrs advertised - and they're probably close to that. I've had my 910xt out to about 8 hrs.

I usually have my progress estimated by landmarks, if they're obvious. Some hybrid races with lots of road intersections are confusing to know exactly where.

I wear a cheap watch and I know the distances for the aid stations. I just do the math in my head. I find a Garmin to be a major distraction (in a bad way) when I run 100 milers.