The weed control and 3ft deep rule is for water with a plankton bloom with water visibility of 2ft. If the water has good transparency of 3 to 6 ft then the 3 ft rule does not apply. Others are correct pond weeds of some sort will grow in or on just about anything underwater; filamentous algae on rocks and vascular plants on sand, mud, gravel and stones once the organics collect and start decaying on the bottom. About the only place under water where the weeds do not grow well is among large rocks, broken concrete and solid rock.
Some sort of ledge or step is necessary to hold rocks - boulders from rolling or sliding all the way down steep banks. The ledge can be created as 'snrub' described or it can be cut into the bank with a small bulldozer by the contractor operating parallel to the shoreline.
