It is possible to use a net to secure a crumbling facade by stretching it in front of the facade to catch falling stones or mortar. This could be especially useful if the damage is on a house facade that is near roads, sidewalks or other busy areas and could pose a danger to passers-by.
However, the net should not be used as the only action to secure the facade. Use this securing primarily to avert acute danger from falling parts. In the medium term, the facade should be repaired or replaced. Until then, securing with a fabric tarpaulin or a net is an adequate first step.