Self Fencing Resource
A Self-Fencing resource is one which automatically guarantees exclusive access to its resource. IBM's ServeRAID controllers, for example, are self-fencing.
Certain other resources (like a Disk Reservation resource for example) can be effectively to fence other resources (like the disk they depend on), can also be considered to be self-fencing, since only one such resource can be logically started at a time.
Self-fencing resources are distinct from resources which do not require fencing at all in order to maintain their integrity.