I have something called redact I think which I saw on tv for farm animals. You pour it along the spine and it is meant to last 6 weeks. Mad mare hates it. Not sure if it works or not. I checked and it was best before 2004, but she can't read ....
ive been recommended Deosect by our local CWG as being the only thing thats any good! Dont bother with anything with Deet or Citronella in! I used the Deet stuff on myself last year. Got bitten 7 times by horse flies in my paddock, ended up with cellulitis!
We used to use cold tea and vinegar. I seem to recall it worked quite well (at least as well as some of the ones in the shops anyway), we only stopped using it because we got fed up with our grey ponies smelling like a chip shop having brown streaks all over them! At least it's cheap if you want to give it a try (could add some crushed garlic as well I suppose for extra oomph).
I used to make one with tea and vinegar and garlic. Left it in the car over the summer and then got rid of it down the toilet in the old Victorian house where I worked, in the attic. It stank out the whole building.
Ponies have got a garlic lick that is meant to be a fly repellent. I've also got Coopers Plus which is meant to be good. The flies aren't too bad around here atm, but I think I may get a fly hood for the sheltie if they get bad and if I can get one small enough.
anyway we won a prize draw at Woodbridge or Poplar or some other local show recently and now have a shed load of shampoos and oils and fly sprays and stuff so might as well use that up first - assuming they don't work it will be a coin toss between deosect and coopers
we made stuff using the Avon thing last year, it kept going all lumpy grrrrr AND IT DID NOT WORK