I have a Garmin Forerunner 305. It works fine for what I bought it for. It is water resistant to 1m. I use it all the time cycling and a fair number of times kiting and once in a mega windy downwinder. They are about $160 on ebay.
R. Naish was using the Garmin Forerunner 310XT. They are waterproof to 50m (dunno if you get a GPS signal at 50m). They cost $300 on ebay. I would buy this one if I was buying a new one.
Here is a track of an upwind run I did kiteboarding while you guys were doing a downwinder. If you see a kiteboard somewhere between Brighton and St Kilda in a northerly then it will be me.

Some stats:
Total distance 53.69 km
Total time 2:17
Max speed 41.4 kph
Average speed 23.4 kph
Average upwind leg: 500 m
Average upwind ground: 160 m
Best upwind gain 450m