When we moved in, eight years ago, the area behind the wall was all gravelled. When I first decided to build a pond I was constrained by two shrubs at the front, and also by the surprise discovery of a very well engineered concrete path hidden half an inch down. The foundations of the path are half a metre deep. Rather than break it up with a sledgehammer, I decided to make a feature of it. However, with that and the shrubs, I ended up with a pond significantly smaller than I wanted.
Subsequently, one shrub died because I'd got too close to it, and the other got far too big and had to be removed. Then this spring I found that the liner had sprung a leak. I was going to have to replace the liner, and I might as well extend the pond nearer to the size I had initially wanted.