peel a little apple skin. use the the apple side and give a smear on lens
Spot on , or eat the apple and lick the lens , stay away from rainex at least test on the back of the case first it can affect some plastic badly , Plexus is a much better option than the rainex.
a drop of dishwashing liquid rubbed into the dome on the housing will give about an hour of protection - it forms a super thin film that water drops become a part of as they hit the lens.
For photos this film does ever so slightly alter the optics of the picture - but for video its not so critical- water drops hit the lens and appear to instantly just be absorbed into the picture.
The saliva trick works too.
i think the apple trick doesnt have enough longevity / convenience for in water use - but might be ok fro occasional spray sitatuations