I've used quitkick and it is fantastic. Horse stopped after one nights use and then only had to use it every six months or so to remind him. When they bang the door the quitkick box sprays a small jet of water at them. Expensive but worth it!
John has trained me for dressage for the last fifteen years or so and my son for eventing -all phases- for the last three. I can thoroughly recommend him both for adults and keen kids. .Very strong on correct basics and good riding. He's great!