Best way to make possums go away, without killing them, as follows:
You will need two posts, they need to have at least two feet in the ground and six feet above ground, preferably set in concrete, four feet apart. Attach two eye bolts to the inside of the posts. Tie three pieces of twelve foot surgical tubing to each eye bolt and braid them, then cut two one foot long two by sixes, nail them to make a L shape. Drill one inch holes in the top of the L, on each side, attach surgical tubing to these holes. Drill a small hole through the top of the L, in the center. Now, about twenty six feet away, sink another post, sticking up about three feet, screw a two foot piece of two by six to the top pointing towards and perpendicular to the other two posts, centered between them. Drill a hole through the end of it. Now get a lawn tractor and pull back the L platform, tie it through the hole in the center of the L to the hole in the board that is mounted on the single post. Use 1/4 inch cotton twine or single strand of baling twine. Important to tie very securely and without much slack. Now lay a concrete block just in front of the L platform to make a convenient little step. Last step is to rub bacon grease or peanut butter into the twine, rub it in good. When erecting this opossum deterrent keep in mind things like the neighbors bedroom window. If they are "good" neighbors, then an effort should be made not to have this pointed directly at their bedroom window, otherwise build as you wish. Another consideration would be prevailing wind, in case you inadvertently remove a skunk. Don't worry, it won't hurt them, their bones are quite dense. It might actually be quite enjoyable for them, as they gain a new perspective of their habitat. Enjoy.