Being severely myopic since age 7 and wearing thick plexiglass lenses since 1950...I am a dang expert. I lost regular glasses only one time, surfing at Makaha when I failed to tie my safety string around my neck before attaching it to the other side. The locals laughed and gave me the stink eye, but did I care? Nah, Brah!

If glasses get salty, first wash them off in (salt) water.
Then to remove water spots- lick them off with a dry tongue. (It's usually most convenient to use your own). THE PLASTIC LENSES NEVER GET SCRATCHED. Croakies are almost always the best, but can wash off over your head if you pearl your board, windsurfer or cat: so loop another breakable string over the Croakie & loosely around your neck.
ALSO- big plastic goggles- BlueBlockers- like the old people wear! Keep the splashes running off your head with a billed baseball cap, and the BlueBlockers will do most of the rest- by keeping most spray off your glasses. You do have 4 surfaces to clean + lick between races on a breezy day, but very rarely get your eyeballs washed out by spray. After racing, hang them off your rear view mirror by the string and they will last for YEARS.
Signed, Lick-M Cowboy. (Demos given at Tradewinds!)