My problem is a bit different than the selective suspend option, I have it turned off, and I still get the occasional turn off, and it often seems that doing anything in another monitor, or selecting a program outside of fsx causes this, but not all the time. I was wondering if there was a 100% surefire way of getting the joystick to cut out? Or is it random with everyone else?

The "consensus" (if you read the joystick mega thread) is that when the main  FSX (or P3d) window loses focus, then the joystick becomes disabled. Most people here have moved on from this issue by either reinstalling Win 7 or using FSUIPC to control the joystick. 

What do you mean lose focus?

When you are running Windows as your OS, only one window can have the focus (meaning it accepts mouse and keyboard commands) at a time and the rest are in the background. If you had a few days to read through the Win 8 joystick mega thread (and I'm not suggesting that you do), you would see a number of comments saying that when the main FSX window lost its focus, subsequently the joystick disconnect occurred. This could happen either by alt-tabbing out to the windows desktop or just by switching between the various views in FSX.

The fact that FSUIPC reads the joystick, while fsx can't should say something, it should mean that there is an alternative someplace that I am just not seeing.

FSX uses a legacy approach to controlling the joystick. When the stick goes missing, it is still working in the Windows control panel.