Stating a discriminatory preference in a housing post is illegal, is prohibited on craigslist, and can be expensive:

• you can be fined more than $10,000 for each discriminatory ad, plus damages in court, plus loss of license if you are a professional
  
  
• avoid phrases which could be interpreted as discriminating by race/color/origin (e.g. 'hispanic area'), religion (e.g. 'christian home'), age / familial status (e.g. 'no kids'), disability, or sexual orientation
  
  
• the words you choose can cost you - get the facts and avoid being prosecuted under fair housing law