By locking do you mean hiding?
I personally use Hide It Pro, it appears in your phone as "Audio Manager" and you can access the actual app via a hidden mechanism and a code.
Link: Hide Photos, Video and App Lock - Hide it Pro - Apps on Google Play
Yes, I want to hide with a password or drawing pattern and only I want to access it.
AppLock used to do it. Now it doesn't work.
Many reviewers using hide it pro mentioned they have lost pics, videos.
Are you facing this problem?