Cats do not pose a threat to adult opossums but the young opossums are at risk. If a dog must stay out at night then try to confine to a run or small section of the yard away from an area opossums may travel. Drive slower at night, preferably in the center lane so you will have more time to react if an opossum crosses the street. If you see a dead opossum on the road then move it to the side of the road, if safe to do so, and check to see if it is a female with young in the pouch. If an orphaned or injured opossum is found then contact the Opossum Society of the United States, a local wildlife rehabilitator, veterinarian, or animal shelter.
Many opossums suffer painful deaths from poisoning.
Clean up any spills, especially sweet-tasting antifreeze. Do not use rat poison. If you suspect an opossum may have been poisoned then contact a veterinarian or rehabilitator immediately. It would be helpful if you have information about the poison, name, active ingredient, possible time of ingestion, and any signs or symptoms displayed by the animal. An opossum may drink from a pool, fall in and drown.