Unusual Question

[Doug Hardie]

I have a FreeBSD 9.3 remote server that needs to be purged.  I know that rm -rf / will remove all the directory entries, but I need to write over the drive.  I thought that dd if=/dev/zero of=/dev/ada0 might do the trick, but it gives an not permitted error.  The whole thing can crash and burn at the end.  This is an unmanned site so moving drives is not viable.