A chainsaw works great for me when it comes to keeping trees short (think giant bonsai, not half a tree and top it early to encourage branching). The roots will keep going, though. Keep the poplars at least 20-30 feet away from concrete and plumbing. Poplar is notorious for shallow root systems and actively seeking out water. If there is a crack nearby the tree will find the water in it and grow there making the crack bigger/taller/deeper. And once there is a giant root under your driveway (right on a seam and lifting one side) getting rid of the tree only slows things down. The giant root keeps shooting new sprouts right on the edge or the cut/concrete. Don't ask how i know this, please. Let's just say stepping down into the garage isn't so bad until you are trying to push something heavy out of the garage and up the 3" step.