I make my Time Machine backups on an external hard drive. Recently I upgraded from Mountain Lion to Mavericks. Now I need the ability to freeze those old backups I've done with Mountain Lion in case I need to go back with the hole system.

What I tried so far:

1. Stop Time Machine and rename backup folder on the disk. On Mavericks the Time Machine folders can't be renamed or moved.
2. Remove the external drive from Time Machine preference pane and read the drive - Time Machine backups continue on same folder and in some time in the future overwrites old backups.

How can I achieve what I want?