Possums are fairly harmless when it comes to attacking humans, but they are a nuisance that can tear apart bags of trash and leave your lawn a mess. Getting rid of a possum is fairly easy, and it takes very little to get rid of the possum without causing it harm. There are poisons and similar items that are available, but these are brutal and entirely unnecessary.
Wait it out. Possums typically do not stay in the same area for more than a few days, especially when no food is available. By keeping all trash stored in a trash can with lid, the possum will quickly leave your property.
Open a can of cat food and place it inside of a live animal trap. This type of trap opens from one side, and when the possum enters the trap to eat the cat food, it will step on a trigger switch that closes the trap and captures the possum inside without hurting it.
Place the trap somewhere near the perimeter of your home, near the area where you see the possum entering the underside of your home. Check the trap twice per day until you capture the possum.
Drive the possum a few miles down the road to a remote location, and carefully open the trap so the possum can get out of the trap.