Hollow trees are Natural habitat of possum but now their natural habitat is rapidly disappearing due to cutting of trees. Due to this they have to adapt to the human house. Because these creatures are very territorial, they are not easily moved, especially if they decide to seek refuge in the attic of your house.
There are some possum removal techniques that can be used to prevent your area from some toxic pests. The possum house can be repaired by a tree in your yard, about four meters off the ground so far from the reach of cats and dogs. You can explore possum catcher in Sydney for getting more ideas about pest removal.
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Use half a banana or apple in a new house for pushing it to investigate. You should also trim any overhanging tree branches or near the tree in order to ensure that it does not have access to the roof again.
Put the light on your roof cavity and keep it for 3 days and nights. This combo of light and the smell would drive most possums out of your roof and possibly into your house built for them outside. So, if you do not hear the possum for a few nights then you have successfully removed. Then, to prevent it from returning you need to block all access points to the roof using chicken wire and wood. The best time to block access is at night.