Snapshot immuatability : how to make it un-deletable ?

Hello.

I browsed around but I can't find an answer to that : how can I make sure a snaspshot is immutable in terms of 1) can not be deleted 2) an other snapshot can not be created with the same name 3) not renamable.

I explored
* (RTC) permissions, behaviors. What am I missing ?
* (Article) Controlling access to source control in Rational Team Control 2.0 with some Write protection scenarios.
* (Forum) Patterns for protecing source code
* (Forum) SCM Best-practice baseline and snapshots
* (Doc) Project and process concepts for permissions and behaviors.

Key words : how to make sure a snapshot is undeletable, write protect snapshot, how to make sure a snapshot is not renamed.

Regards.
G.