Measure the perimeter of the garden you are creating a rock border for. Take note of these measurements when you go to the garden supply store to select the stones - the stones must fit snugly beside each other and cover the entire perimeter.
Spray paint around the perimeter of the garden indicating how wide the stone border will be. The width of the border depends on the size of the stones being used.
Clear the area between the garden and the spray paint line. Use a shovel to dig a few inches underneath the grass, removing the sod. This will give the rocks a slight trench to sit in and will make sure the rocks are set in place
Place the stones in a line from one end to the other, making sure each one fits snugly against the next. If you are using oddly shaped river stones you might have to use the trial and error method to find two stones that interlock together.