At dusk the tide slides under the Dosoris causeway and the light stretches long and gold across the water. Beaver Landscapers Corp works the lawns on those lanes with weekly mowing, trimming along fences and stone walls, edging, and the cleanups that open and close the growing season. Salt air and shade from old trees make north-shore turf particular; it wants cutting often and never too short. Little beats pulling out of a driveway at the end of a route and seeing the lawn lie flat and even in that low sun. Glen Cove and the small roads running off it toward the shore fill most of a week.