By October the ridge above the Cal-Sag turns every shade a hardwood knows, and every one of those leaves eventually lands on somebody's grass in Palos Hills. That is one season of it. The rest is the long green run from April on: weekly mowing, edges cut in along drives and walks, trimming where a deck cannot reach, borders kept clear of whatever is creeping into them. Sid's Unlimited Landscaping runs that circuit through the southwest Cook County streets, and the measure of a good day is a row of yards that all look deliberate from the curb. A lawn is the first thing a house says to the street; it may as well say something tidy.