Getting a sun dial to work on a hill is a bit of a challenge. My wife designed a terrace for it and my son and I built it in two days with one day spent getting the materials. We used four inch cube Belgian Blocks and no cement; but, we did use a silicon glue for strength. The glue went on easy and was clean;but the smell is very bad.
First we carefully measured and then built a prototype by laying out the blocks next to the herb garden. Then we dug the foundation, used crushed and powder stone 2 inches thick as a foundation.
Now we laid in the blocks keeping things on the level and plumb.
The TOH wall tip to plumb the walls is critical as well was making sure things are level at every stage. See the picture. The sun dial works when there is sun. The herb garden is beautiful and my wife is happy.
The total cost was about $200.