Garage retaing wall

[syne]

So originally a retaing wall was going to be built 1400 high on the boundary line and the garage wall  was going to be independent.

 

The se however suggested that if the ground could be sloped the garage wall could be full filled with concrete and build regs would satisfied, structural calculations unneeded and thousands saved.

All good, but leaves the perennial question of damp proofing..

Insulation is going on the inside face of the wall.

 

My last retaining wall had bitchumin coated on the back, fabric wrapped  perforated drain and gravel fill. But that was a patio wall in a garden, it's performed well and the render hasn't blown 3 years later 

 

What would you do here?

I can't dig any further down as its solid rock and a soak crate is  going to be a right pain to do as It'd have to go 20m away in the garden to get it away from boundaries and buildings..

 

But I am going to put a roof/shed along the gap between the garage and the fence.

It'd very well protected from the weather.

Should i tank it it?