Well, the walls were necessary regardless of if there was a water feature or not, The property has a weird elevation change where the SE corner is the lowest point and the NW corner is the highest, so we've got a half walk-out basement. Because the highest point on our property is also one of the lowest points on the neighbours property we ended up needing a series of concrete walls if we wanted any level space in our backyard. The terraces were necessary due to building codes about wall height, and thus through happy accident I got a perfect place to put a water feature
But yes, the backyard has more concrete in it than the rest of our house. That was painful.
I also meant to mention that I think I'm leaning towards the new Ecotech Radion LED's for lighting. I would need 6 units I think to cover my tank, which is not a small investment, so I've been following Mr. Saltwater Tank's experiment with them before I commit to anything.