Final answer:
Option 1: Visual - K-9 unit involves conducting visual and K-9 searches around the perimeter for secondary devices.
Step-by-step explanation:
The option that involves conducting visual and K-9 searches around the perimeter for secondary devices is Option 1: Visual - K-9 unit. This option utilizes the assistance of K-9 units, specifically trained dogs, to search for explosives or illegal substances in public facilities.
For example, K-9 units can be employed at train stations or other locations to detect any potential threats. These dogs have a keen sense of smell and can identify hidden materials that may pose a danger to public safety.
By combining visual searches with the expertise of the K-9 units, law enforcement can enhance their ability to handle potential threats and ensure the safety of the community.