1. As far as I am aware it is impossible to permanently deepen your voice. The method I use lasts for roughly a day and a half before my deeper voice fades away and the exercise must be repeated.

2. I've been doing this exercise once a day 3-4 times a week for over 2 years and have never had any problems with or damage done to my voice. No one I've ever shared this exercise to has ever done any damage either. That said, I make no guarantees as to that here, do this exercise at your own risk.

How to Instantly Get a Deeper Voice

Step 1: Tilt your head back as far as you can.
Step 2: Recite the sentence "Bing, Bong. Ding, Dong. King Kong." slowly, stretching/elongating the "ng" sound for each.
Step 3: Repeat step 2 but at a deeper pitch
Step 4: Repeat again, this time at your deepest possible pitch.

Congratulations, you now have a deeper, manlier and sexier voice. At least for the next day or so. Enjoy