i have used both glasses and contacts. when i first started i would wear the same glasses i wore daily, but then i got a new pair and used the old for boating. never lost a pair in 3+ years, had a good strap system (not croakies). then i got a pair of rx safety glasses that were good and nerdy looking. i lost them the first time out - my old strap wouldn't fit, so i put some croakies on them for my first run of the year on gunni gorge. lost them in the first swirly play spot, and had to run the lower half of the run blind.
for the past two years i have been wearing contacts. i keep my eyes closed when rolling, and wear sun glasses that keep the wave splash off my eyes. i have never lost a contact. my contact rx is the same in both eyes, so if i loose one i can move the other to my dominant eye (right in my case) and see enough to make it home. if i lost both i would be screwed.
i actually prefer wearing glasses, and i would just splash my face regularly to keep them clean and fog free. i also feel my vision is more precise through glasses, as that is what i wear all the time. i only wear contacts when biking, skiing and boating. whatever strap you decide to use, include duct tape for added security.