My horse is the same. Bombproof with all traffic except tractors. In the past i have tried walking around stationary tractors with carrots balanced on them, among other things but nothing really worked so I just accepted it.
I left the dressage one because it seemed to be made up of really good riders who had bought horses with problems for next to nothing and trained to PSG in next to no time. Made me feel completely inadequate!😂
This one is in Botolph Claydon in Buckinghamshire. No personal experience but have seen the horses grazing in the fields and they look well cared for. I believe they only take in horses a couple of times a year and there is a waiting list...
I used arms and legs. I dont think you need to give yourself as much time as a horse. My leg went very strange - numb and tingly when I did three hours! Obviously as per the instructions you are not supposed to use the horse device on humans!