Middle Englishfensen,derivative offensfenceentry1 First Known Use Noun 14th century, in the meaning defined atsense 1 Verb 15th century, in the meaning defined attransitive sense 1a Time Traveler The first known use offencewas in the 14th century ...
Since around the 1980's "ring-fencing" has been primarily a financial term, but the roots of the term are in the ring of fencing put around an area of land to confine livestock. So its core meaning is "a comprehensive barrier protecting" something. In the quote cited, I believe "ring...