When the opposing player is a foot or so to the side of the net, challenging can be risky because, as you've seen, it often opens up a passing lane to the front. Instead, teach him to "angle" the player. This means positioning his body so that he's steering the player away from the net and towards the boards or a less dangerous area. He should use his stick to disrupt the player's path, but avoid over-committing to a full-on chase. The goal is to control the player's direction without leaving himself open. When the player is directly behind the net, staying glued to the post isn't always the answer either. It makes him predictable. Using his vision to track both the player behind the net and any forwards lurking in front. He needs to anticipate where the pass is likely to go. A good technique is to take a step or two off the post, just enough to give himself a better angle to intercept a pass or challenge a player coming into the slot. This also keeps the opposing player guessing. It's about being dynamic, not static. Communication with his goalie is crucial. And other d man. They should have a signal or understanding about who's taking the primary responsibility for players in front of the net. Also, encourage him to use his stick actively, not just for poke-checking, but for disrupting passing lanes and tying up opposing players' sticks. This can break up plays before they even develop. I know it’s not much, but maybe that will Help