Lift up with your inside hand to tilt his nose around instead of allowing him to use so much of his body. Tilting his nose in will but his balance to the outside shoulder more, and you'll have a better follow through from behind. It'llbe a little difficult at first, but if you take the pattern at a slow canter, you should catch it pretty quick. Good luck :) Posted via Mobile Device
Use your inside thigh to push that inside shoulder into the outside rein, then use outside rein to steer him around the barrel. If that doesn't work don't cue him for the turn until his haunches are at the barrel (instead of when his shoulders are at the barrel.