when I first installed Fences i left the options at the default settings.
In the Back-Ups group "Preserve my layout by scaling my fence groups" was checked
But, the sub option of "when I plug in a new primary monitor, move my icons to it" was not.
After I watched the video posted earlier, I checked that option also. It did affect the result but it did not fix it.
But I also tried the option "Store my layout on a per-monitor-configuration basis"
and this option seems to be the way to go as the fences retained their positions after reboot.
Ive only done one reboot and one total shutdown, BUT the fence locations, docked at the bottom+roll up survived the reboot and were in the correct positions. I'll wait a few more days to see how it goes.