Rod Stewart has vowed to get a vasectomy - after he fathers one more child.The legendary rocker - who already has seven children with five different women - says he would love to have a little girl with fiancée Penny Lancaster but would then call the time on becoming a father.He said: "One more child and I am going to have to close the office. A girl would be nice."Rod - who has a ten-month-old son Alastair with Penny - says he is planning to tie the knot with the former model before they try for their second baby.He said: "We're going to get married next summer - we're not sure where, but definitely next summer."The 61-year-old also told the US TV show Entertainment Tonight that Alastair has been the first person to hear songs from his next album, as he sings them to him before bedtime.