There have been v.accurate GPS in small form like smart phones for years, accuracy depends on the manufacturer not size. Also many smart phones are not only oleophobic(sp?) Oil repellant but hydrophobic. So a bit of water is no problem at all. My moto g is one of those and there are plenty of vids demonstrating there capabilities.
As for watch GPS I sail tsers cats use paddle boards bicycles bushwalk etc and they would all be GPS watch activities. The price for an accurate one and the hassle of a wristband are the con's. In the end I think id wait till the smartwatches with GPS , phone and basic attributes of a smartphone are reasonably priced, then I'd seriously consider handing over the $s. Think about it, not only could you brag that half knot more but you could call your mate out on the water just to rub it in.