If you have a hard time following through or you stop your follow-through, then you need to do exercises to increase flexibility and mobility around your spine. Your ability to take your hips and spine through full range of motion will extend your follow-through and improve your clubhead speed. This exercise will loosen up back muscles so that it will be easier to follow-through.
Start on all fours with your back flat.
Slowly slowly round your back and look down, hold stretch for a moment.
Return to start position, then slowly arch your back and look up, hold position for a moment and return to the start position.
Alternate between arching and rounding your back.
Do 8 to 10 repetitions.