Why is "the guardian" wrong ? http://www.wordreference.com/gren/%CF%86%CF%8D%CE%BB%CE%B1%CE%BA%CE%B1%CF%82
If you check the reverse translation you will see that guardian is προστάτης = protector rather than guard.
filakas is also referred to as a police officer
Ποιά είναι η θηλυκή μορφή της λέξης "φύλακας";