Ok, since we're talking snake oil.....
I will 'fess up that I tried a "urban legion".Two years ago I was preping my prop for coats of barrier coat 2001/2002 and a guy walked by.He offered that his solution worked great for the past 5 years. I tried it, and had varying results.His method was to combine cayenne pepper with Desitin ointment and coat the prop, shaft, and depth transducer.The first year it worked great, the second year- not so great. I think the difference was in the boat usage.The first year we spent 5 weeks cruising to and from Maine and another 4+ weeks going to the Chesapeake. Our home port was Westerly, RI.The second year (last year) the weather was SO BAD that our sailboat sat on it's mooring for 4 weeks at a time for 3 times!! After each 4-week non-use period, the prop was fouled. And the bottom was poor at haulout too.I also added cayenne pepper to my bottom paint for the two year period. Very clean the first year, poor the second.I conclude that the best and maybe only way to keep a prop clean is to use it.This year? I'm planning to go back to a barrier coat and regular bottom paint. However, an Interlux sales rep suggested that I only coat and paint the prop on the hub and out to 1/3 of the blade length. He claimed that the barnicles won't stick on the tips and by not painting the tips, I won't have paint and barrier coat that will chip off and then require stripping and re-doing.I've tried the outdrive spray and the barnicles seemed to think it was FOOD! Worst results I've ever seen.Honestly, I don't think anything really works to prevent prop fouling.