I carry my Macbook Pro (15" Retina, Mid 2012 with Mt. Lion) between my work and home. It is connected to an external HDD as a Time Machine. I always forget to properly eject the HDD before putting my notebook to sleep (I rarely shut it down) at my office.
Is there a way to have it prompt with a custom reminder or warning when I try to put MBP to sleep, using Automator or something?