Better to leave external drives unmounted when not using?

I had an external drive fail last year, and now I back up every day to two different drives to that it never happens again. I have a true phobia now.

now obviously drives fail. it just happens. but can I prolong the inevitable by not having them mounted and appearing on the desktop when not in use? and only mount when I need to access a file from the drive? or am i doing more harm by turning it on and off a few times a week? is it better to just leave all of them on for good?

thanks