Rocks that are placed in rock gardens are not a standard shape, but usually fairly irregular. You can compliment this irregularity by adding a geometric fountain. Rock placement is best with the long diameter neatly horizontal and parallel to the face of the slope, appearing as if they had just fallen from the mountain and landed this way. They can be set wth the long pieces in the bank to lock the pile securely into place also. You should never place the long axis vertically, as this just does not form naturally.
Also, plants cannot grow on a pinnacle. They create stumbling hazards, and can become loosr and fall on your plants. You want your garden rocks to appear to have solidarity. Each rock should be locked into its position by its own weight or its relation to other rocks, so it cannot move, even during the seasonal changes of rain, frost, snow, etc. While to rocks are being places, a man with heavy tread, should put his weight into the rocks to make sure they are locked.
If any of your rocks should slide, tilt or move in any fashion, they need to be pulled out and reset. Repairing your rock garden can be very difficult and exasperating, especially once your plants have begun to grow. Rocks will slip if they are left to move. This is why the placement of each rock is so important.
To create stability it is normal practice to lay the larger rocks on the bottom, and move upwards with successively smaller rocks. This ensures a firm position, while still allowing room for plants. You must strive for meeting the requirement of plants. Plants will not grow in air pockets, so your skilled stone mason, must also do the work of a gardener. It is usually impossible to convince a "walking delegate" that placing stones for a rock garden is non-union labor.
Cement is not to be used, except for Chinese rock Gardens. Soil, instead, is ram packed into ever crack and crevice. There cannot be any holes; they need to be firmly pack with soil, so that every bot of earth has a direct connection to the soil beneath and even down to the subsoil below the new construction.
Wherever one large rock goes upon another, the poor roots would be rather squeezed unless chips an inch or more in thickness take the weight from the soil strip. Egg-like pebbles used as chinkers will give the garden a rocking, rolling motion. Save up broken bricks for flat laying and wedge-like chips for the uptilting next in order. Except in rare cases, all horizontal crevices should be far from level but sloping downward into the bank (never forward downward), with the front of the rock so tilted upwards so that rain runs easily down into the crevice.
This requirement is for the health of your plants, and not a rule of geology or art. The rocks will need to tilt back from 10-45 degrees or more, but each higher rock will need to be set back off the lower rocks line, creating a back face for the whole wall slope. This way each plant will receive air, light, water and room to grow. Use your person judgment to vary the angle and line of the wall face to avoid the appearance of regularity.
Remember that all vertical fissures need to be V-shaped, so soil can rest firmly against the sides leaving no air pockets wherein roots will shrivel and die. When large crevices are to be divided, the stones should be wedge-like and dropped in large end down , which is quite unlike the usual way of burying stones, so that the fissures may be still V-shaped from above.
