The PanelView Plus isn't good at security at all, and there is no activity monitor either. You can't even see if the screen saver is active.
Best bet, if you are controlling security from the PLC end, it probably means that you don't have a lot of controls that are secured. In a situation like that, with Control/compact logix level PLC's, the best method I've found is to start a "Logout" timer when the secure password is enabled in the PLC.
Then every (Secure) PVPlus write to the PLC, use the Enter connection, and Enter key handshaking. Use the handshake to reset your timer.
For digital writes, just put a reset command for the timer in series with your logic.
PITA? Yep, but it works.