Every time I take my GoPro out... I'm disappointed when I get back home. So many awesome shots ruined by fuzzy blurry salt stain right over the action. How do you keep your lens clean...????
Rinse the lens, spit on it, rub it clean, rinse Similar to swim goggles. My problem is I keep bumping it and causing the mount angle to change, and not noticing it until way later.
try these i use them on my sailing glasses works a treat , $5 from chemist warehouse 
But you may not want to lick it afterwards! 
