the garmin etrex series, and i presume other waterproof garmins, are water resistant to 1meter for 30minutes, IPX7 i think.

1 meter, 3 feet, is not very deep and if you are punching off a board into the water the water pressure on the case can easily be equal to 2 or 3 meters

so for windsurfing you really do some kind of flexible sealable clear case

having said that i use my legendc and vista hcx on my cat and on my kayaks without any case as they are hard to read and work the buttons in a case. lots of splashing and a couple of capsizes later they have had no water problems

the newer hcx series seem to have a solid alloy battery door which looks more waterproof than the plastic door on the legendc. the battery door seems the weakest link in the waterproofing

the etrex series have a lot of display options and so far i've found it best to use the navigation screen switched to big numbers and then select max speed, speed and speed again as the 3 things to display. speed twice so i can see it at a glance

garmin support have been very good to me over the years sending me parts to reseal my 2 year old venture after my baby daughter bit a rubber switch cover off and repairing my out of warranty legendc when the usb chip fried due to me using an unfiltered cable to power it from a car lighter socket

both units bought via ebay. however it has never been an automatic free repair. i have had to email a few people in marketing and be very nice and polite. it may help that i contribute a lot to 2 garmin forums

i don't know much about the forerunners but the color etrex can do screen grabs which are much easier and clearer than just taking pics of the unit, have attached a screen grab here