Another possibility is Marion Wickert, in Burscheid.
She is a veterinarian an is working nearly exclusivly in handling aggressiv and/or difficult horses.
Including horses, which you can not handle after "Elite-Auktion"(german) or things like this. She has worked with circus Knie for one year in training "Steiger"(german), stallions.
You can call her up. 0049/2175/88 88 60.
If you want to know more, tell me which kind of difficulty you have with your horse.
I also can find out an adress in Switzerland. He is a physiotherapeut treating painfull an therefore aggressiv or buckling or running away horses.
Dr. G. Bauer