Well, I hate whips. I very seldom ever pick one up. I have not even had a riding crop or whip for at least 5 or 6 years. I keep a 5' stock whip around but seldom pick it up either. If I do, it usually has a plastic sack tied to the end of it.
If a horse gets mad at a whip (one of the reasons I hate them) it is because the handler / rider just 'pecks' at the horse with it. Anyway, whips make things worse instead of better many times.
I use the long ends of my split harness leather reins. I will spank a horse's butt with an 'over and under' action and do it hard. I have never had a horse require more than one reprimand if I did it hard enough the first time.
Nagging and pecking and swatting a horse is the worst thing one can do. They just get mad and more spoiled. If I ever have to get after a horse, I want him to think that he is lucky to be alive. Then, I do not praise him or do anything else. I just ride on like absolutely nothing happened at all. I've never had to discipline one twice if I did it right the first time.