Three dominant operators with sticky customers and steady cash flows look built to outlast market cycles.Investors hunting for "forever" stocks should start with businesses that are difficult to displace. The best candidates pair scale advantages with recurring demand and customer lock-in, allowing them to compound earnings through business cycles and return excess cash along the way. This summer's earnings season offered a fresh read on three companies that fit the bill: Waste Management (WM -0.96%), Intui ...