to protect a person, place, or object by staying near them and watching them:
The Sergeant told Swift to guard the entrance.
a lioness guarding her cubs
guard somebody/something against something
There is no one to guard these isolated farms against attack.
to watch a prisoner to prevent them from escaping
to protect something such as a right or a secret by preventing other people from taking it away, discovering it etc:
chiefs who jealously guarded their independence
to prevent another sports player from gaining points, getting the ball etc
guard against somethingphrasal verb
Exercise can guard against a number of illnesses.
guard against doing something
Nurses should guard against becoming too attached to their patients.