After years of swatting flies and failing to find any home remedy that did much, I decided to comb the internet for an effective fly repentant... and found catnip oil!
Recommended by the Department of Agriculture and EPA as an effective replant for stable flies, I don't understand why it hasn't made it to the mainstream for boaters. Plastic-safe (no risk of melting vinyl windows with a hand-print), people-safe, cheap, easy, effective, and pleasant, it is everything that DEET is not. It only lasts about 30 minutes, but we can live with that. Often the flies just leave, when we take the food source away.
To our great relief, our cat was not interested in our legs after returning home.
Try it out, and report back if you find a more potent version!
$5.99 for 8 ounces from Petco.