A good exercise is to set 2 oxers, and allow one stride in between. Make the first a ramp oxer, and the second a reverse ramp oxer.
(A ramp oxer is when the first bar is a few inches lower than the second, creating a "ramp". A reverse ramp, you guessed it! Higher first bar).
The ramp oxer will encourage the horse to bring his knees up higher, and keep his lower leg tighter. As a result, he will land deeper after the first fence, causing him to need to sit back and rebalance for the second. The higher rail in the reverse oxer will cause the horse to sit back and judge the fence "measure" it, if you will) which sets him up for a tighter front end over the jump.
But, as jeddah said, just getting him off his forehand first will help the problem. :)
"The white horse moved like a dancer, which is not surprising: a horse is a beautiful animal, but it is perhaps most remarkable because it moves as if it always hears music."