GBDE - Destroy command not working

[Dany Nativel]

I've been playing around with GBDE under 5.2RC2-1. It's a fantastic 
encrypted FS.
Following the man page, I've tried to use the destroy command but 
without success.

Here is what I did to create the encrypted FS (for this test I didn't 
use the /dev/random to fill-up the disc).

# kldload geom_bde
# gbde init /dev/da0 -i
# gbde setkey /dev/da0 -n 2
# gbde attach /dev/da0 
# newfs /dev/da0.bde
# mount /dev/da0.bde /mnt/usbkey
--> use the FS, works fine
# umount /mnt/usbkey
# gbde detach da0

Then according to the man page I should use  :
#gbde destroy da0 -n -1   to purge all keys but I get :
gbde: illegal option -- n

so I changed to :
#gbde destroy da0 --n -1   and got  :
gbde: read: Innapropriate ioctl for device

so I changed to :
#gbde destroy /dev/da0 --n -1  and this time I get the password prompt 
but it fails to destroy anything :
Enter passphrase:
Opened with key 0
gbde: No -L option and no space in sector 0 for lockfile

Maybe I didn't understand the purpose of the this command. I thought it 
was going to replace each lock key with some random data.
Can somebody explain me how to use the "destroy" command ?

Thanks
Dany