The WinTec (10Hz/5HzSBAS) also has a place for lanyard loop so it will attach to a keychain as long as you can thread something through it and link it on the chain.

It is also marketed as being "waterproof", but I'd say water resistant and you might want to make sure you keep the USB cover/plug or insure it was covered if it ever was immersed. But it is far better than the other inexpensive GPS units I've seen - there is a rubber like coating which forms a gasket.