Within the Parental Menu, arrow to the right and select the Edit Locked category. The Edit Locked category allows you to lock specific channels. This will require you to enter a PIN in order to view programming on that channel.
A list of channels will display. Use the Up/Down arrow buttons to move through the list of channels. When you arrive at one that you want to lock, press the OK button, and the channel will be added to the locked list.
When you are finished making your selections, press the Blue button on the remote to lock the selected channels. Press the Red button on the remote to discard the changes and return to normal viewing.