Stop a network drive from automatically mapping

Solution 1:

How are you unmounting? Have you tried simply:

net use /d z:

Solution 2:

From How to connect and disconnect a network drive in Windows XP:

Disconnect from a mapped network drive

1. Double-click My Computer.
2. Right-click the icon for the mapped drive.
3. Click Disconnect.

If it still returns, do :

net use /persistent:no

and then reboot. When you now log in, all of your mapped drives should be gone and you can remap the ones you need.

Solution 3:

Remount the drive as before, but leave the "[] Reconnect at logon" box UNCHECKED. It will give a warning, but replace it anyway. On the next logon, it will be gone.