[apalrd]

As long as you never write the SD card, then the SD card's wear leveling feature shouldn't try to move blocks around.

This requires:
-Disabling swap entirely (it's generally a good idea to disable virtual memory entirely on real-time systems anyway)
-Mount the SD card as read-only
-Mount the temp directory onto a RAM disk

There are some tutorials on the internet explaining this, there are a lot of nuances since a number of automatically installed packages will try to write to disk (including syslog and fake-hwclock among others). Once you take care of all of those, you can set the fstab to mount the partition as read only so no program can write to the disk.

It's certainly possible for a carefully designed system to be turned off by pulling power. Virtually all embedded systems including the roboRIO operate in this way.