I have weekly flatwork lessons with a dressage rider and instructor. That was the best thing I ever did. Last night was our first lesson for the year and I couldn't believe my horse was doing the movement he was, I got scored 9 out of 10 for out extention!!!! Yes he picked up his feet!!
Do raised trotting poles awell, if you want him to pick up ghis feet do trot poles then lift up one side on one pole then the next on the other side and so on. It helps