Hi George,
I'm pretty sure you'd be fine with the diluted citronella oils that are found in non-chemical bug repellents for horses. Online you can find remote training collars that are for gently spraying a dog when it's misbehaving - many of them contain a citronella solution-as it is distasteful to a dogs sense of smell.
But I'm sure mixed in with other herb oils it wouldn't be half as distracting, and better than the flies
.
Let us know how it's going!
Blue