Geometry: setting out a circle without access to the centrepoint

I have to set out a garden wall which is a true arc, but the centrepoint of the arc is inaccessible (it is inside the house). Using basic equipment such as string, nails, stakes, straight-edges, etc, can anyone suggest a practical way to accurately lay out the wall?

Now, I know I can extract distances from a drawing and mark those out, say, every metre from the back wall of the house, and then fill in roughly by eye. I want to do better than that. Any ideas?