need Keep the FMC constant on another screen

hi guys

i have 2 separates screen and i undock the fmc on one of these screens.

but when i change the camera to the outside and come back to the cockpit need to reundock th FMC again.

i need to keep the FMC constant on the separate screen.what i need to do...(some times undock another panals and he same thing occure.)