How to Seal Your Home
Sealing up your home, also called an exclusion, is vital to keeping more squirrels and other wildlife out of your home going forward. This process requires finding any and all potential entry points and sealing them so that no other animal can gain entry. All animals will leave behind a scent trail - pheromones - that other animals can follow, and if the squirrel was in your attic these will lead other animals right into your attic as well.
You should always start by looking for more obvious entry points first, these are typically roof returns, pipes, vents, and any obvious holes. You should then go over the home again to identify any smaller holes that may have been missed. Your best method for sealing these is to put a wire mesh over the hole and enforce it with bolts. This makes it almost impossible for animals to pull the wire off, and very rarely can they chew through it.
If you have noticed that you have wood or soffit damage that may not be able to be fixed easily, you should contact a contractor to give you an idea of what you should do to fix it. These can be major entry points for different kinds of animals, so it is important to get it fixed as soon as possible.
You should get the exclusion process done as quickly as possible once the squirrels are gone. You can even start it when they are still in the attic, as long as you do not seal all holes and trap them inside. Which would be bad, because they would end up passing away and leaving you with a terrible odor.