Amy I can totally relate to your frustration and paranoia with this!
We have a roommate who "forgets" to close the front door behind him all the time. It doesn't have a real door knob, you have to really pull the door closed with this little handle thing.
Well, he likes to just swing it shut and hope that it sticks but it rarely does. OK, it's bad enough that that means he's not locking the empty house when he leaves, but it also means one day the dogs could get out and be GONE! Thankfully they've always been found when he's done this but still, I am way paranoid anytime he is going in and out of the house doing stuff. Sometimes I'll even put P.C. in the garage and Smokey in the backyard or his crate. It's just too risky!
He's moving out in December though... Phew.