Just about any really high SPF, waterproof suntan lotion will work - lather it on. I like the coppertone baby suntan lotion, spf 50 that comes in a pink bottle - holds up really well.
A couple of things to note, the bastards usually only will bite your legs, make sure you wear wading pants when you fish the flats. If you are fishing on a flats boat, wear thick WHITE or light colored socks to protect your feet (or use the above mentioned lotion). Last thing, they prefer dark colors and just because you are fishing off shore doesn't mean they won't find you. Wait until one flies down your snorkel.....
All winter I wear shorts, all summer, I wear long pants during the day -- ooooh, I hate those bastards.
They hurt when they bite, they stalk you even if you go under water, they are right there. They are annoying, but less so in other islands.
They can be really bad some days, not so bad others. If you head to the back county - way up one of the creeks or up in the bights or to the west side - they can be really annoying. I've had days when the inside of my boat looked like some sort of massacre had occurred. Other days, just a few. The worst I ever got lit up was when pulling anchor after snorkeling - they seemed to just know I couldn't get them.
Women seem to suffer the worst - they try to just lay out and the flies will get them. If you keep moving they aren't too bad.
But, I did have one bite me while I was riding a bike once......
I never encountered them on any island other than Andros.
Horse Fly, yellow Fly, Doctor fly, they are all pretty much the same.
They are also called deer flies.
They are on all the islands and are worse when the wind is blowing from the land side. A good repellant is vanilla extract which works for mosquitos as well. I do know that real extract as opposed to immitation works better.
Another hot tip for keeping those pesky reglular black flies away from your food while eating in the islands is to rim your plate with hot sauce; I guess they don't like the odor/fumes which it produces.
old trick I learned long ago was with a old captain that only used noxema cold cream that the girls use .. it has eucalyptus in it and it has the ability to keep the bugs a foot away from you and it does not burn you like deet so you do not have to worry about putting it on your ears and neck.. or having to use it and sit on a plastic chair.. try it it will work good for you.. remember though that the new fish skinz or sun socks also keep the sun from hurting you.