Thanks Leo and Jon, that worked well for me.
If anybody is wondering: the script for preventing locked tabs to be closed, can be found here: Acecool Proper Tabs - Prevent closing locked tabs - #8 by na4raitda
Look at Leo's post in that thread if you also want to prevent them closing when you press ctrl + w.
Perhaps I might suggest considering making ctrl + tab the default for cycling through tabs (and ctrl + shift + tab for cycling the tabs in the other direction). It seems to be the default way of doing this in Windows applications.