Allisa, mustard oil and don't let him lick it??? Stop dog from licking ????? Huge leather muzzle maybe???, I am sure the dog would love that, maybe as much as the flies, and of course the dog could get the added bonus of getting it into his/her eyes. I think I might be taking it serious when I am supposed to view it as humour. My solution, let the dogs stay in the house during the day, they love it and then at night put them back in the outside kennels and listen to them complain about not being in the house LOL. Those flies are bastards of things, biting the dogs' ears etc, what a mess they make and how dreadful for the poor dogs. Seriously, MINT plants are supposed to keep flies away. Surprisingly in my country NSW location I have not had a lot of trouble over many years with flies bothering the dogs, not sure why ????? It was in Sydney where I recall them being very bad and vicious. I always had MINT around my kennels in country location but I can't assume that this is the reason the flies were not a big problem.