I use Deep Woods Off aerosol. When the flies show up in the cut I douse myself with it. Keeps them away for long enough. It seems, though, that with the repellents you apply to the skin, their effectiveness depends as much on individual body chemistry as anything else. What works for one person doesn't work for the next, and vise versa.
I also second the Off Mosquito coils- we use them at rest. They keep pretty much everything away from the boat.