DPMS won't disable

[Grant]

I'm using this to disable DPMS but it isn't working:

Section "Monitor"
        Identifier "Monitor"
        Option "DPMS" "false"
EndSection

I can disable it manually with 'xset -dpms' just fine.  I tried
disabling lightdm and xfce4 and using startx but DPMS is still enabled
in that case.  What am I missing?

- Grant