Forum:Defender the Magical Knight

My friends and I had a 2v2 game yesterday where some controversy was sparked over Defender, the Magical Knight (my card). They debated the once per turn rule stating that if I used the block on openient A's turn, that I could not use the block again on openient B's turn because it had not became my turn again and the effect had not reset. My side of the argument was that each of their turns counted separately and I could use the block on both of their turns because the card states "once per turn" as in for each openient's turn. Could someone clarify this scenario for me?