Ring fence
From ACT Wiki
1.
To legally separate particular assets or liabilities within a company or other organisation.
For example, to shield particular assets from the claims of the creditors of the non-ring fenced part of the entity.
In the banking context, a 'ring fence' is the separation of some aspects of commercial banking (mostly retail) into a separate entity to reduce the probability of failure.
2.
The legal barrier created for this purpose.
Sometimes written "ringfence".