This achievement can be obtained by completing the 'Trouble With Clones' missions there is 3 missions in total there is a more in depth guide on how to get all missable achievements i suggest looking at the walkthrough for the 360 version as its the same and it gives a better guide
Saints Row: The Third WalkthroughThe 3 missions you need to complete and they are Weird Science, Tour de Farce and Send In The Clones your final mission will be you protecting Johnny and will end on the bridge so once you complete that mission your achievement will pop but as i said there is missable achievements that i haven't mentioned that is in the walkthrough!