GM without others seeing it via the Guardian...
All Discussion is Public, the Guardian was meant for the GM to inform you about something that is happening to your Character that the other Players should not know. What you want to do is change the typical design among Players by carrying out actions unbeknownst to them. That will require extra Membership capabilities to facilitate what you want to do in this Community:
For two way Private communication you need to Donate
towards a Premium account which will open up that facility as well as others. At the same time you will also be monetarily contributing to the extensive work and resources that goes into a site like this. Note:
The GM will also need a similar account to see your message. See the Compare Membership
page. You can negotiate with your GM to see if they will also Upgrade to facilitate you.