Crystal Barricade : "Prevent all noncombat damage that would be dealt to other creatures you control".

Technically, this means that the only way to destroy a creature (other than Crystal Barricade) in this case is by using a spell that has the word "destroy" or through combat damage.

A player used the card : "Wick's Patrol" : "When this creature enters, mill three cards. When you do, target creature an opponent controls gets -X/-X until end of turn, where X is the greatest mana value among cards in your graveyard."

The opponent was able to use this card on my Ajani's Pridemate, successfully killing it. However, Wick's Patrol's ability triggers noncombat damage, which should have been blocked by Crystal Barricade.