IPhone 5s :: Can Lock Mail Access

More and more our phones are becoming communal devices, we lend them to friends, family, co-workers to make calls, play games, share information and numerous other activities. He works in an business area where information security is at a premium. As such he doesn't store any secure information on his phone. Â

I totally understand and respect his decision, however there's an Achilles heel to his methodology. Like most business oriented people the main flow of company information comes in the form of email. Not getting that instant access on your phone can be a detriment. Currently when he has down time he'll open up a browser on his phone and log into his webmail. It works, but it's just not as effective as having the email on the iPhone and having the alerts. My question being, is there a way he can lock down his mail? Is there an app that would require an additional password to open Mail? Or is there an option so that the Mail can only be opened with a fingerprint?

Info:
iPhone 5s