### Clue: Loudly advertise second-class anti-flood construction (4)
### Answer: BARK 
 ### Explanation: Definition: Loudly advertise 
 B(signifying second-class, as opposed to A, first-class) + ARK(Noah's construction to beat the Flood).
Defn: As done by the person in front of a show, fair, carnival booth, to attract passers-by.