How can I stop phone from showing locked app's main screen in 'recent?'

[AC Question]

I am attempting to lock (password/code protect) an instant messaging app that no longer offers the capability to sign out, so I am always signed in. I have tried several lock apps, and with each one, I have run into the same problem. If a person is unable to open the locked app, the app then is listed/shown as a 'recent' app with NO LOCK on the initial screen, thus revealing messages on the first page, defeating the app lock.
I also tried 'hiding' the app with Nova Launcher prime but was unsuccessful. I've been working at this for many hours and would love any assistance. Thank you in advance.

LGL22c
Android version 5.0.1
Kernel version 3.10.49

 

[B. Diddy]

Welcome to Android Central! Try this thread: http://forums.androidcentral.com/android-4-1-4-2-4-3-jelly-bean/265491-hiding-app-recent-button.html