A good emergency repellant, is good old fashion mud. I was stuck lying prone for a good hour being eaten by a swarm of them. I was wearing bug spray, but smearing dirt and mud on any exposed skin prevented them from landing. It also absorbs sweat, sticks and cools you down, stops the itching of previous bites and camoflauges you.
Not recommended if you dont like getting dirty.
Before the internet, the village idiot would stay in his own village.