I'm also just starting out in this forum
Here we go then.
Why don't you use some contexts to illustrate the meaning and use of the expressions like:
He always prefers sitting in the back of the car (and
not behind the car)
(I don't think it is used too often in different contexts than vehicles
: see below)
You can find the table of contents at the back of the book
Imagine a few rows of people one behind the other. Jack is standing at the back - you can see his head sticking out.
You can also take this opportunity to explain
on the back of (if that's not too confusing after all)
There was a sticker on the back of the car which said: Follow me if you can
You have to sing you name on the back of a credit card.
These contexts should let your student get a grasp of how to use the expressions
(Except for all that you can say
He was shot in the back of his head or
This thought was always there at/in the back of my mind - but it's more like a fixed phrase this one)