A "secure fence" refers to a strong and well-protected barrier or wall that is difficult to breach or scale. It is designed to keep something or someone safe and protected from external threats or intruders. Full definition
They are highly energetic as well, meaning they need an active owner who knows how to handle this breed's need for escaping with a well secured fenced yard. (dogsora.com)
We have a very secure fence but I have no doubt that if she were let off the leash to roam freely, she would dig under the fence in less than 2 minutes. (northeastanimalshelter.org)