we looked at a homeowner's yard to give a quote. the front of the house is only 25' from the front sidewalk, 30' from the street, with a fairly large backyard. the owner said "the last 3 lawn service companies brought in these big commerical mowers and every one of them went very fast and sent rocks into my front window. there must be little rocks from the street in my yard. after breaking a window twice last year the last guy started putting up a cover over the window when he came. i haven't heard from him yet this year." i suppose previous companies have given up on this customer. how do i keep from sending little rocks through the window? slowing down the throttle/blade speed to the minimum? higher or lower cutting height? something else?