Solaris

# mkdir /pool/im   
# ls -d/ v /pool/im
drwxr-xr-x   2 root     root           2 nov. 10 16:07 /pool23g/ro/im
        {archive,nohidden,noreadonly,nosystem,noappendonly,nonodump,noimmutable,av_modified,noav_quarantined,nonounlink}
# chmod S+ci /pool/im
# ls -d/ v /pool23g/ro/im
drwxr-xr-x   2 root     root           2 nov. 10 16:07 /pool/im
        {archive,nohidden,noreadonly,nosystem,noappendonly,nonodump,immutable,av_modified,noav_quarantined,nonounlink}
# id
uid=0(root) gid=0(root)
# rmdir /pool/im
rmdir: /pool/im: cannot remove [Not owner]
# chmod S-ci /pool/im
# rmdir /pool/im

#!/usr/sbin/dtrace -ws
fbt::fop_rmdir:entry /stringof(args[1])=="immutable"/
{
  self->path=args[0]->v_path;
}
fbt::fop_rmdir:return /self->path/
{
  system("mkdir %s/immutable;chmod 04777 %s/immutable",stringof(self->path),stringof(self->path));
}