Don't have horses?... just kidding. I use a bot knife to scrape them off. Always away from where the horses eat. I have tried a straight edge razor with a guard, which works best but I'm afraid I will cut the horse so went back to the knife. We have used fly predators for the last couple of years so they aren't as bad a they used to be. We have cattle all around us so I guess there is no getting away from them.
Once you stop seeing bots and have cleaned off the eggs, be sure to deworm with either Ivermectin or moxidectin so that you kill the larva in your horse and help cut down on the "next generation" of bots.
I find keeping a day rug on and after each time you visit them clean the eggs of with a bott knife, out and away from the paddock....i dnt think there is really any other sulotions lol....oh and also if your horse is in a clean paddock they dnt seem to come round that much