I've thought there have been times when Harry should share SOME secrets with SOME characters. Harry would have to be judicious in what he revealed and to whom, but the tendency of Harry and White Council members to jealousy guard most secrets seems incredibly counter productive when the secret you know provides little context for understanding its meaning and no ability to gain allies who might help you in the long-run. (Yes, Harry let the Erlking know that his mother was Margaret LeFay, but that seems a really minor secret to me; even if we hadn't learned that Lara already knew this.)
What I was thinking after reading Battle Ground is that during their final conversation, Harry might said something like this to Carlos:
"Warden Ramirez, before you leave I have one last thing to tell you. You're right, I have been keeping secrets from you. I swear to you, sharing any or all of them with you couldn't have stopped what happened here tonight. I know that doesn't satisfy you so I will share this with you.
You know how I exposed Peabody as a traitor at Warden Morgan's trial. What you don't know is that I held back some vital information in my testimony. There was another wizard with Peabody when he attacked members of the Senior Council on the island out on Lake Michigan. I don't know who it was, I just know there was another spellcaster there. In fact, for all I know it could have been you, though I don't believe that. Now if you think I'm lying to you, you have no reason to report what I just told you to anyone on the Council. If it's a lie, then it would be useless information, wouldn't it? But, if I'm telling you the truth; and I swear 'Los, by my magic that I am, you can't tell anyone else on Council what I just told you. You could be reporting this to the very traitor Peabody was working with, or they might tell it to the traitor and in either case your life expectancy would probably get a lot shorter. Maybe one day we can talk about this some more, but for now you know some of what I have had to deal with. Good luck Warden."
Perhaps that would be too dangerous to share with Ramirez, but at some point Harry is going to have to move beyond his self imposed boundaries and start trusting someone.