By Julien Pretot MONT ST MICHEL, France, June 30 (Reuters) - Defending champion Chris Froome looks set for a rocky ride with an army of hungry rivals trying to prevent the Briton becoming the first rider for over 20 years to retain the Tour de France. "This is the toughest challenge I've faced in my career, to target a third Tour de France," Froome, who prevailed on the French roads in 2013 and 2015, said. Team Sky's Froome, who won the Criterium du Dauphine warm-up race earlier this month, proved last year that he could be impervious to outside pressure, hanging on to his lead despite the media attacks and those coming from the crowd, which included having urine thrown at him during one stage. More...