Bi-directional Sync

I need help writing a simple rule to keep my iMac and External Drive in sync. I plan to start out with a mirror copy of the iMac Documents folder on the External Drive.

I normally take the External Drive with me every day and use it to access any files I may need while away from my iMac.

Sometimes I save new files to the External Drive's folders. Sometimes I modify a file already there. When I return home and connect it to my iMac, I want to be able to move those changes to the iMac.

Sometimes I make changes on the iMac files and/or folders, too, and I want to be able to move those changes to the External Drive.

I take care not to change the same files and/or folders on the devices at the same time, so as not to create a conflict.

Most of the rules I've read on the forum have to do with basic syncs. Not sure what I want to do is considered 'basic', but I'm sure Hazel can do it.

I just need help with specifics.

I assume I need a rule that watches the Documents folder (and all its sub-folders) on my iMac and the Documents folder (and all its sub-folders) on my External USB Drive), but am unsure how to go from there.

Anyone have suggestions, or a rule that works and mind sharing it?

If there is any information I left out that is needed for your input, let me know.

Thanks!

Bi-directional sync is quite tricky and I would not recommend using Hazel for that. I would seek out a tool specifically made for that as you need a mechanism to handle conflicts should they occur.