The frightened animal will freeze and not move. Sprinkle flour around the entrance to check for tracks to ensure the opossum has left. Once it leaves seal the entrance. Make sure there are no young left behind before sealing. If it is in your garden it is helping you by serving as your free gardener, eating the harmful pests that do damage.
Opossums prefer to eat overripe, rotting fruit that has fallen from trees.
You probably would not want to eat this fruit. Keep opossums out of trees by cutting branches near walls fences, roof and the ground. To discourage climbing, wrap the tree trunk with heavy plastic or metal sheet or cut out sides of a large plastic trash can. Join the Opossum Society of the United States. Raising infant opossums and rehabilitating injured opossums is expensive.