Securing your content in your mind.
Rehearsing your presentation is actually two activities:
1) vocalizing to make fragile content secure &
2) practicing your speaking swing in order to develop control.
Let's talk about the first:
To secure content, approach it in downloads – units of thought that go together as one idea/message. One download at a time, talk through the idea out loud or in your head over and over letting the language evolve as you hone the idea. This is not script memorization. This is refining the shape, size, texture, etc. of the idea so that you can easily express it on demand under any conditions.
The cool thing is that you can secure content as you exercise, take a shower, drive your commute, etc. and you can do it in your head.