I love this expression "ring fenced". It keeps cropping up in management-speak bull**** propaganda , but I haven't a clue what it means (along with most other people I suspect) - if indeed it means anything at all. How, or indeed why, would/could anyone put a fence around a slot? Wouldn't a fence obstruct the runway/apron, or whatever other part of the airfield that a slot inhabits?
When people use this type of expression it means they are talking through their 'ring' themselves.
As the senior native English speaker in my old department (sorry, business unit ....) I used to attend meetings ( ... debriefings) and pretend not to know what they were on about when they started with this bull****.