My roofing contractor wants to put TPO membrane on the flat roof of my house. It is a 2600 sq ft surface. I am concerned that the squirrels and crows that are often on the roof will pick at the TPO and damage it. The squirrels have been very destructive to my wood fence, plastic garden edging, and gnaw at the end of the PVC pipe that drains the AC unit condensate. Do they attack TPO? I have read that crows pick at it but the source might not be reputable.