How do I grant irrevocable privacy from user with sudo access? In Unix, any user with sudo access can act as any other user using sudo su. This invalidates any imagined privacy of local files for all other users of the same Mac. Is there any (preferably OS-level) way to work around this and give users of a multi-user Mac privacy from a potentially snooping administrator?

Edit: In my further testing it seems at least Keychain is blocked for the administrator using sudo su. Using security I could see the metadata -- i.e. what websites there were passwords for and titles of secure notes -- but not the contents themselves. And even if I as administrator reset the account password, the login keychain still used the old password. Also of interest, opening GUI apps using open will try to open them for the actual user(in their GUI context, and only if it exists), not in the GUI context of the administrator.

Edit2: To get into the right frame of mind, imagine a family with one Mac. The kids have been learning about root access and are asking how they can be sure Mom &amp; Dad can't snoop on their files. How do Mom &amp; Dad avoid buying one Mac per kid?
Basically all files stored locally are accessible by an admin user (or any user who can run a root shell). This also includes locally stored/cached files held in Dropbox, Google Drive, iCloud etc. 

If a user wants to prevent an admin looking at his/her file, he/her should create an encrypted DMG using Disk Utility, should not store its password in the Keychain and should take extra care to always unmount the DMG whenever he/she walks away from the computer.