Full swing · Changes the swing

Tee gate around the clubhead

Setup in 3D
3D view
Setup from above
From above

Push one tee in just outside the toe and one just inside the heel, with room for the clubhead. Hit the ball without touching either tee. Narrow the gate when you pass four of five.

Trains
Heel, Toe, Shank
Dose (suggestion)
3 sets of 5 balls
Count
Shots through the gate without touching a tee, out of N
Stop signal
Stop: pain 3 out of 10 or more, pain spreading into an arm or leg, numbness, or more pain the next morning.
Source
Golf Digest: Hank Haney, test your impact