When defending a corner kick we all like to get close to the near post of the goal. I used to get really close to the near post until a college coach taught me this strategy. Stand about an arm length away from the post (into the field). When the ball comes across close or curves towards the goal you have you other hand extended outwards. If it flies past your hand you will know that the flight of the ball will be beyond the far post. If you can deflect the ball, be sure you 'punch' the ball away from the goal mouth so there is no secondary shot on goal.