Careful when you pull the ticks out, the head must not stay under the horse's skin!
I'm used to use apply natural solutions so I know the geraniol. It dehydrates ticks. You can even do your own solution with black olive oil soap and geraniol. The soap
makes the geraniol non-irritating :)
Repulsive products aren't always the solution as some can have bad effects on horses because of the components. I have heard about the geraniol, this substance is naturally present in some flowers. It is a good and especially natural repulsive. You can find some in shop!