In every single picture of me paddling, I'm wearing my Silverfish S-Rat Surf sunglasses. EVERY. SINGLE. PICTURE. I got them about four years ago when I was learning to surf. I couldn't see anything–I'd never been able to see anything while swimming. In a pool, that wasn't a problem. If I needed to look for waves to catch, that was a problem. I looked online for a lot of different glasses and somehow decided on Silverfish. I've never been disappointed.
I've worn my S-Rat original model glasses to surf (or, more accurately, to thrash around in and out of the water) in hurricane swell and they've never come off my head. Or broken. I just got a new prescription so I ordered the S-Rat II models in tortoise. I have a pretty major prescription, and many sunglass companies won't touch it.
I don't know why more people don't know about them, or why they don't seem to have many "pro" riders. Maybe they aren't flashy enough for some people. For those of you who can't wear contacts and for whom glasses are a matter of life or death (i.e. you can't SEE AT ALL without them), these are the real deal, and I highly recommend grabbing a pair! They look fine, but more importantly, they stay on your head in everything. If you don't have a sunglass sponsor and can't lose a $200 pair of sunglasses every time you go windsurfing, check them out. My pair with some bells and whistles (polarized, fast lab, etc.) was less than my regular pair of sunglasses.
The adjustable strap in the back clicks into the ends of the frames. You could unclick the strap and wear the glasses "normally" if you wanted to.
They stay on no matter what you’re doing.