Special dua for married men

From the duas of Muhammad bin al-Munkadir (ra), a famous muhaddith of the tabi’een: 
اللهم قو ذكري فإن فيه صلاحا لأهلي
“O Allah! Strengthen my private part for in it is a rectification (i.e. keeping in line) of my wife.”
– Ibnul Qayyim (rah), Rawdatul Muhibbeen.