May I quote from the great man....

"....In both these cases, the basic problem is that at the moment of impact the player's hands - and therefore the clubhead - are further away from the body than they were at address. Certainly, shanks can result from standing too close to the ball to begin with"....blah, blah...."But normally it is simply a case of one's weight shifting forward out towards the toes, throwing the hands and the clubhead further away from the body"....."The instinctive reaction is to stand further away from the ball"....."WRONG. That actually compounds the problem, as it forces you to reach for the ball through impact, pushing even more weight forward onto your toes".

Two drills.....
1) in severe cases place a ball under the toe of each shoe
2) Use a two ball drill......put one ball on the ground (tee/mat) and another half an inch outside your object ball. Try to hit the inner ball without dislodging the other. Simple, and perfect

I've only ever used the two ball drill.....but anything that stops you falling towards your toes is going to fix the problem.

Good luck.