I have tested a new guard for the outboard propeller - first in slow water. The guard of this type in USA is called Mac’s River Runner. I have bought it from the firm Laguna (Khabarovsk).
The guard is welded out of stainless steel
The prop guard is fastened with three screws
The propeller is protected from the rocks and pebbles
My inflatable boat with Tohatsu 9.8 motor could run up to 31 km/hour; with the prop guard attached the maximum speed with the same load was 27 km/hour. Some power losses caused by the guard are visible; I still plan to use it in shallow rivers.