Wickr is a messaging service that uses two way military grade encryption with a private code so that your messages are 100% unrecoverable. Even if forced with a warrant, your messages will be unable to be decoded. Also has a "Secure Shredder" that forensically wipes your phone of all deleted data. Good luck, be smart.
Textsecure is very similar but is it open source and audited. No destructing messages though, you need to delete them yourself.