If you use the Kurtis specs with the leash or with a helmet you wont lose them in the water.
I have inspected the bowels of overhead surf with the Kurtis specs on and never lost them.
Now trying not to lose them with a car full of kiting junk when car pooling with 4 other kiters is another issue
No need to use Rain-X or anything like that.
Keep in mind that some rain-x will get into your eyes when water splases around in them... not good.
Better than Rain-X there is a wax product you can use. Better anti-fogging than Rain-X.
On the down side Kurtis specs arn't available with prescription lenses.
With the cheap ebay specs you are risking an eye injury if the frames break in a crash.