I use Repel-X. I buy the concentrate, mix it myself, then spray it on a washcloth and wipe Christy throughly. It is supposed to last for 2 or 3 days. Usually it does, but the flies are soooo bad this year. I have to wipe her down every day. Doesn't totally stop them, but I usually only see 1 or 2 flies on her, and sometimes they don't bite. If they do bit her, the repelent kills them so at least that one doesn't come back! It works well with goat flies (little tiny flies) house flies, and horse flies. Also works with misquitoes and ticks. You can also spray it on, but I prefer to really wet her coat with the wipeing, it seems to be more effective.
For me, I get out the Off and spray myself.
I think flies need a new name: Mini Vampires!