There should be a way to prevent new members from unlocking doors and chest of promoted members of the clan. For example, only the clan leader can open everything while the promoted clan members can only open their own chests and that of the new clan members. This should also apply to doors. Also, new members should not be allowed to destroy buildings that were not built by them in the clan. That will avoid creating potential grieffers!
That would be too far I think, when you recruit people into clans there is always a risk. This is a reason that many don’t join or want to be in clans. Espionage is a viable tactic in any game of war. I have played lots of games where the best way to beat other teams is to send in a spy and have them ruin things form within, its a viable game tactic and occurred in real life. They changed it so that players need to rank up to access vaults I believe, so there is some access restriction now. I do think there should be personal buildings or items that you can create that are exempt from clan ownership in case you get kicked or just don’t like the current clan and want to leave.