I grew up with one in my house and we only ever had our own cats use it. We had raccoons in the area and I don't think they ever found the entrance and the cats wouldn't use it around them. My grandmother lived more out in the wilderness and she had a skunk come in, and I think she had a deer try once. So there is a chance that something will come in. It should come with a removable cover so you can keep the cat in at night and that will reduce the chances the wildlife will come in.