Marigold... how to make a spray?

Hi everyone!
Well, as I'm guessing some people know, marigolds seem to keep pests (flies especially), away.
I make my own flyspray, but it's way too harsh to spray near my horse's head, which is where all the nice ear/eye/nose flies like to huddle.
There's a company who makes marigold spray, and it's gentle enough for the face. However, it's also at least $20, and while I'll pay it if I have to, I'd much rather make my own.
The thing Im having trouble with, is how to do it.
I know that olive oil, mixed with the flowers, will do it (tincture or something?), but I'd rather not spray oil on my horse's pink skin, and then let her sit outside in the sun. (Cooking her is not on my To-Do list.)
Making a tea, somehow?
(As you can see, I'm very new to this, lol)
Any help at all would be appreciated.
(Lol, even though this is now in the pest catagory, it's not actually about pests. I'm simply asking how to get marigolds into somekind of spray, tea, ect., which doesn't seem particularly 'buggy' to me...)

Something i do with my dog, because here in the Artic the flies and mosquitoes are deadly,,lol. just kidding, but it feels like it. I take some tops of the plants, you want to use marigolds so take the tops and rub in your hands, rub your face then the horses and take off riding. the natural oil will come off the flower but not burn your skin from the sun, like the commercial oils will.

I use catnip on my dog, because it repels fleas, flies and mosqitoes. I also have a live plant near his bed or i take dried and put under... also i use the plant the same way as the you would the marigold, i rub it on his bed. He can then sleep fly free. try hanging some around your horses stable bed. i promise it will work.

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