2. Go to the page at http://www.livejournal.com/admin/console/
3. In the box, type ban_set [username] but exchange [username] with the person you wish to ban.
4. Click "execute."
5. That person will now be unable to post to your Journal until you use a ban_unset command. (You can also deactivate bans on your Edit User Info page.)
...and yes, this does go quite nicely with the friends-locked entry I just created.