I've written a lot lately about learning to use your hands better in your golf swing. This GC video from Mike Bender caught my eye because it's a unique approach to correcting faulty hand action.
The drill for correcting a slice -- gripping your lead hand by REALLY putting your trail hand underneath it -- is very interesting to me. If you wrap your trailing fingers underneath enough that the tips of those fingers are on top of your lead hand knuckles, you won't need much effort to close that clubface!
It works because this drill forces your lead elbow closer to your side during impact, so you use your entire arm to square the clubface instead of only your hand. That's the proper way to do it.
The drill for correcting a hook -- taking a split grip and using your trail hand to aim the clubface -- sounds to me like a sound approach to the problem. But I confess that I've never had a problem with a hook, so this drill may seem more effective to me than it will to some of you.
However, using your trail hand to hold the clubface open is probably the most consistent way to create a fade. Many players instinctively over-rotate their lead forearm when they try to square the clubface with the back of their lead hand, so splitting the grip gives your trail hand more control over the clubface.
I really prefer using drills like the L-to-L drill as your first line of attack for correcting this kind of problem, but these two drills may help if you're really struggling to control a curve. After all, the L-to-L drill mimics a regular swing. I doubt you'll try to hit balls on the course using the grips in Bender's drills!