Make disk completely read-only?

[Sam Zehr]

Hi, this is Sam again, working on making a USB flash drive in FreeBSD 9.0
_completely_ read-only.

Disk is mounted read-only - fstab has ro,noatime

Following some advice from the list, I've done some binary compares to see
what is going on. It looks like only a few bytes are changing every time I
reboot, they seem to correspond with the superblock locations - I would
guess a timestamp of mount time?

I executed the dumpfs command after a few boots, and checked for
differences. The only thing that is changing is from the first line

Pass 1:
magic	19540119 (UFS2)	time	Mon Jul 23 11:12:06 2012
superblock location	65536	id	[ 4fe363f7 e7fd3a99 ]

Pass 2:
magic	19540119 (UFS2)	time	Mon Jul 23 11:28:35 2012
superblock location	65536	id	[ 4fe363f7 e7fd3a99 ]

Does anyone know of a way to stop this timestamp from occurring?

Sam