set up journaling on root partition

[h bagade]

hello everybody ,

i want to enable journaling in my FreeBSD8.2. in freebsd handbook,
journaling is done in single user mode by unmount desired partition and set
journal for it by "gjournal label" command.
this manual is ok and works well far all partitions except root because
root partition can not be unmounted in single user mode.

i try different ways to set journaling for my root such as : do
partitioning in by gpart in fixit mode and then try to set journaling for
my root in this mode. but error occurred and journaling is not done.

please let me know what is the correct way to set journaling for my root
partition? do it in single user mode or fixit mode? how?

i'm trying to do it more than a week but no success:((
any comments or hints are really appreciated.