Busy Ext. Hard Drives?

I use my ext. hard drive mainly for backing up my data disk so i only need it plugged in once a week to catch up on updated data on my computer. An annoyance that happens a lot is that some program (probably not the back up software as it was long closed) is holding the ext hard drive from being unplugged (software wise) I could always look at the light on my hard drive and say well it's not blinking therefore it is not reading or writing to disk so it could be safe enough to unplug (physically) but there has always been the myth that doing so before Windows says "it is now safe to unplug the device" will damage the device or lose data. I have done this before but i don't want to make a habit of it.

The other day, something, i don't know what, made me do an anti-virus scan (Avast AV) on the ext- hard drive (i actually started it for a few files and then stopped it rather than doing a complete scan) believing that the AV scanner would release the files from what ever program is using it and it worked! only tried it once but why not try that next time you get locked up? My theory is that the AV stops all other applications from accessing the disk or files so it can prevent viruses or bugs from sending data or spreading if it needed to remove it. My theory about the lock up is that Windows is access it, maybe system restore or something but like you might have noticed i used the word theory, i barely know how AV or Windows software works.

By the way i use Avast AV in my ext. hard drive scenario so i don't know if it will work with others.