This can be practiced as a backhand drill or as a visualisation. Place markers in the shape of a diamond as shown in the animation. The task is straight forward. No balls are allowed to land inside the diamond. By keeping your shots outside of the diamond, you increase your chance of dominating your opponent.
Try to adopt the mentality that every ball must be hit with a purpose.
Even if the markers are not present, visualise the diamond and register when your shots fail the test.