Smartphones have become ubiquitous business tools for attorneys. They are often a means of accessing confidential documents that it may be helpful to share with another party in court or elsewhere. A lawyer may be reluctant to hand a device such as an iPhone to someone else, even a client, when that device can contain so much business and personal information
The good folks at Apple have a solution to this problem. In recent iOS systems you can enable guided access under Settings ... General ... Accessibility.
After turning on Guided Access you need to set a six digit passcode. After it's on anytime you have an app open and you triple click the home button you enter guided access mode. It will not be possible to use another app without triple clicking home again and entering the passcode.
You also have the option to circle areas of the app screen you want to prevent someone from using touch control on.
... and also set a time limit on how long the app can be used for.