Adjust your pressure. Big strong guys like to push and maintain. In martial arts there is an excellent tactic where use an opponents strength against themselves. Apply physical pressure to battle for a position body to body, then release the pressure, then re-apply it but constantly changing. This tactic of adjusting body contact pressure makes it difficult for post players to keep balance.
Poor balance leads to poorer shooting percentages.
The two remaining defenders zone up in the foul lane. Change which players run and double to make it more difficult for a post to kick the ball consistently to the same player. If the big man likes to put the ball on the floor once or twice to get make their offensive move, teach a delayed double team, where the double comes and pinches the ball as the ball hits the floor on the first dribble by the big man. The above tactic is especially useful when you have a post player who is a dangerous scorer but a poor passer out of the trap. Play front the post, and double behind, leaving one weak side defender open until the pass out and across, at which time you close out and match up.