Oliver is a very clever cat. He recently has learned to open the front porch screen door by pushing against it. We place an old shoe and rug against the door to keep it from opening easily but those things are no match for a determined Oliver.
Once he gains access, the door closes behind him and he's trapped until I let him back out. There are days when I come home from work to find Oliver camped out on the front porch.
I'm still working on a fix to this. We have the ability to latch the door to secure it but the problem is the mailbox is on the inside of the porch, so the door must be unlatched during the day so the post-person can deliver the mail.