I have started using Clicker training on my mare. its a long story but to put it briefly- 6 very sucessful trainers have said she is untrainable, crazy and needs to be put to be pts, she was even used in a Monty Roberts demo 2 years ago. last winter after many ckecks for physical problems (there are none) even my vet said she should be destroyed because she had become so dangerous and agressive.
However, I couldnt give up and using Clicker we have had so much progress and huge huge changes. i can catch her, pick up her feet, groom, etc. I am even taking her for walks and will start lunging and long lining soon. I am hoping if we keep making progress I'll be able to ride her!!!
It has made all my horses so much more willing and interested in what they are doing because they have to think more for themselves and the best bit is its so much fun! you can teach basics or advanced schooling and also silly things... im teaching mine to kiss me at the mo! another great thing is that it works best if you do it in short but regular chunks, really great for the winter months when light is scarce.
I am learning with my trainer who used clicker for everything up to very advanced levels of dressage and she recommended I look at the "clicker center" website. you could also try Zen Clicker horsemanship site. I also spent some time on Youtube looking up clicker videos. or you could search on Amazon for a good book. To be honest thiugh, one youve got the idea and have taught your horse the basic lessons you can make it up as you go along and teach all sorts of things.
Sorry for the marathon reply!
Good luck with it and have fun!