If you have rats, you should call your county vector control office. I understand they don't do much about 'possums, but you should ask them before you take any other action, just to make sure you don't inadvertently do something illegal.
If you have 'possums, you can check with nearest state Fish and Game office. They might even provide traps for you ... but then again, maybe not. I don't know about your area, but up here, 'possums don't actually live in trees. They can probably climb well enough to get up a tree when threatened, but I have never seen that happen. 'Possums prefer to live in ready-made ground-level burrows and holes, especially under buildings.
Another place to check with is your nearest wildlife rehabilitation facility. Here in Oregon, we rarely would go out to remove nuisance animals, but we often were able to provide information to property owners, so they could handle the problem themselves.
Trapping is the only method I know of to remove 'possums from an area. I will say, however, that attempting to remove small wild animals from one's property is pretty much doomed to failure, unless you want to make a lifelong hobby of it. As long as the property is attractive to the critters, the removal of one critter will just encourage another to move in.
The real solution lies not so much in removing the animals themselves, as in making your property less attractive to them. Sometimes that is easy to do, just by removing obvious food sources such as pet food left outdoors, fruit that has fallen to the ground ('possums have weak jaws and teeth, and are very fond of overripe fruit!), compost piles, and access to garbage. Other times, when there is a lot of wild food available, the task is impossible. If they're actually living under your house or outbuildings, then blocking up any entrances should encourage them to move elsewhere.
Last edited by Kisal
on Sun Jan 10, 2010 2:47 pm, edited 1 time in total.