It's good to keep your animals safe.
Sheryl has a dog that likes to play outside while she is at work.
Sheryl wants to let her dog play outside while she is at work.
Sheryl installs a doggy door so the dog can go between her house and outside.
Sheryl locks her dog outside while she is at work.
Sheryl's dog can go inside if it is in danger outside.
Sheryl's dog can't get inside the house if it encounter danger outside.