Ticks aren’t just in tall grass - they like to live in wooded areas and crawl up bushes and wait for a victim to pass by and attach to them. It’s not just deer but also all rodents like deer mice. I have had more on me than the horses this year from crawling into my wooded places to water plants. They really really ick me out! I broke down and put all 4 cats on Revolution Plus which has kept ticks off them.
I think the fly spray system going off 6x a day gets enough fly spray on the horses to deter the ticks. But off season when it is not going off I try to fly spray at least every day and use OFF wipes in the base of the tail, down the tail and on the crest of the neck. I have had OFF spray give a bad reaction years ago when I sprayed it on the tail and the spray got on the inside of the thighs. But that is the only time.
And years ago I was boarding at a small place that was next to a state park and it was crawling with deer. And ticks. I asked a vet about sewing cow ear tags to my horse’s fly boots. He said pyrethrum ones were fine but not to use organophosphate ones. That seemed to help with the ticks crawling up his legs and the horse did not have a reaction.