Trail Leg

I have an athlete who instead of bringing his trail leg in the proper movement out to the side, with his knee in the armpit, he brings it underneath his body, with his toe down. He has done drill after drill and does it correctly. He gets too much height over the hurdle and when he lands in turn loses speed. What other things can I have him do to correct this problem? He has good speed and flexibility. Any suggestions?

It could be a method of counteracting other movements either with his upper body or his lead leg. Anything strange there?

Yes his arms are all over. He is a right lead leg and his left arm, when his trail leg is coming through, goes behind his body. He is not very smooth in anything he does and we drill and drill and drill and he looks great but as soon as he starts going over back to bad habits.