Dead Space

Late entry from me... though this won't solve your problem as will just create more spoil... but I always think there is something lovely about a raised pond where you can sit with your nose almost in the water watching the pond skaters!  Because the back of the pond would be level with the ground, wildlife could still get in.  You could use a rigid liner so the weight wouldn't be on the wall.

Just what i would be tempted with!

some prostrate rosemary would take the edges off the wall as well.