Here's two photo's of BJ Watling's defensive technique.
This picture is of his normal block shot. You can see that he has a very loose bottom hand. The bottom of it is so far forward of the bat that you can't see the grip.
|Bottom hand is loose on the bat handle.|
This next one is the ball that he edged and was dropped at slip. Here you see that his bottom hand is tightly onto the bat.
|Using hard hands to defend.|
I'm not really a batting coach, but this is something that young batsmen should learn. If you are going to play a defensive shot, make sure you keep your bottom hand loose. It means that if you edge it, then it won't carry to the slips.