According to the experts, one of the reasons for a slice is that you have an outside-inside swing. There’s no questioning the fact that an outside-inside swing will put side spin on the ball creating a slice. However after analyzing hundreds of golfers I have yet to see a true outside-insight swing.
I have found that in order to get the club head outside most golfers lose their balance and most overextend the arms in a forward direction. This means that instead of bringing the arms down after taking a backswing they must swing the club head in front of the body and then down and across. This is a weird movement that golfers typically do not do.
Another reason suggested for the slice is that the golfer holds the clubface open immediately before and during contact with the ball. This puts side spin on the ball resulting in a slice. An open clubface at contact is well known to be a cause of the slice.However, correcting it still for the most part remains elusive.
Some pros state that you should bring the right foot back in your stance so that you limit the body rotation. This however is a poor fix, especially when the true cause of the slice is insufficient rotation of the arms to square the clubface. Changing the stance by bringing the right foot back gives you less power and creates other problems.
Most effective is to analyze the movements that you make in the swing to see where the problem lies. Usually by determining which actions you are not performing and then doing specialized strength exercises to give you the ability to execute the correct actions, the problem is fixed! The key is to find the main problem from the beginning and not create a new one to resolve an old one.
See Explosive Golf for more information.