On the subject of locking cameras: If I decide to render a scene from the camera view, I switch to that view and use the zoom and pan controls toset the camera into the position I want. Then if I have a character or creature I want to look at the camera, I select the eyes and set the "Point At" parameter to that camera. When I go to the Render feature the default perspective view setting will usually reactivate, so I reset it to the camera view again.

I rarely have more than one camera for a scene unless I want to do an animated scene that switches from one camera to another. 

As for locking a camera into a position, I never do that, since I have not really had a use for a camera to be locked in a certain place.

Just thought I'd throw that in for you.