I have an EOS 760D (recently upgraded from a 30D - yay!), and I'm can't find the custom function that allows you to use back-button AF. Does the 760D have this feature at all or has it been omitted? If it does, could someone point me to the menu item that enables it?
Go to page 357 of the 760D manual. You need to use a Custom Function to change the AE Lock button to a Back Button focus button.
Use C.Fn-10 set to option 1.
Here is a video that also describes how to do it: How-to back button focus on the Canon T4i, T5i, T6i, T6s
The current 760D manual does not have 357 pages. Make sure you are in manual mode then under Custom Function IV scroll along to Option 10 where you will find the screen shot as above.