ringfence

Short definition from Wiktionary

Noun

1. 1
   A fence which encircles a large area, or a whole estate, within one enclosure.

Verb

1. 1
   To guarantee the safety of funds or investment. In particular, to ensure some degree of distinction for monies, that may provide immunity against untoward financial claims.
2. 2
   To specify that funds may only be used for a specific purpose, especially government funds.
3. 3
   To require workers to remain in (particular types of work), as during wartime.