A Four Nights Protocol
If you know of k = 0 (mod 3) cheating husbands, fire on the first night
If you know of k = 1 (mod 3) cheating husbands, fire on the second night
If you know of k = 2 (mod 3) cheating husbands, fire on the third night
If your husband cheats, shoot him on the forth night. (There is at least one cheating husband. So, if shooting occur only on one of the first 3 nights, all of the husbands cheat .)