I've not taken my GPS diving yet, but I did test drive my Otter Box at the weekend.
Otter Box (link) makes a cases that, they say, works to 100ft and is suitable for diving.
I wasn't brave enough to take a GPS out on the first dive, so I stuck a tissue in it and took it down to 25 feet at McAbee beach. Tissue came back to land perfectly dry. That's a good sign right!
Just so you know: A GPS unit will not work underwater. GPS (Global Positioning System) devices rely on signals from satellites orbiting the earth. The signals from the satellites cannot be received underwater. So my plan isn't to have the GPS unit track my dive under water, that won't work! I just want a way to have the GPS with me underwater, so that when I get to an area of interest I can reel the GPS up to the surface, get a GPS fix, then reel the GPS back down.
I have a nice little Garmin 401 GPS, which fits nicely into my Otter Box. I think it's safe to take it with me on the next dive trip.
- Otter Box Waterproof case: $20 REI
- Garmin 401 'Hiking GPS': $150 Amazon.com