ring fence 
noun
1A fence completely enclosing a farm or piece of land.
1.1An effective or comprehensive barrier: he did not say when the merger would be completed or when the ring fence would be abolished...
- The consequence is that the ring fence around the single market is only as strong as its weakest link, and that there is no second chance to impose limits on goods coming from a third country.
verb (ring-fence) [with object]
1Enclose (a piece of land) with a ring fence.I have no problem with the County Council taking over the harbour if the Minister ring-fences the harbour land so that it is only used for the development of the harbour and is not sold off to pay a pension fund or benchmarking pay increases....
- Important recommendations on which no action has been taken include the abolition of stamp duty on motor insurance premiums, or at least ring-fencing such revenue as well as a switch from insuring drivers to vehicles.
- A decision was taken to ring fence the 28 beds in the orthopaedic ward so only patients having elective hip and knee surgery were admitted to the ward.
2British Guarantee that (funds allocated for a particular purpose) will not be spent on anything else: the government failed to ring-fence the money provided to schools...
- This weekend, O'Keeffe said he was concerned that some of the public money ostensibly ring-fenced for the events centre may have been used to finish the previous project.
- Whilst ring-fenced, the funds have not been debited from the card.
- Investments like unit trusts are ring-fenced and are therefore not affected by these matters.