Definitions of ring-fence
to enclose a piece of land; to prevent something (especially a land development) from getting any bigger
A ring-fenced parcel of grazing land is situated between the villages of Rusper and Newdigate.
to guarantee that money intended for a particular purpose will not be spent on anything else
We are calling on the UK government to ring-fence fuel duty for investment in alternative transport.
to guarantee that something (especially an official project) will be protected from destruction, loss or harm
The new UK regulations require banks to ring-fence their core UK operations from their riskier investment banking activities.