This has worked for me for the past several years but you will need a workout partner. I use my wife to spot me:
Three times a week:
I sit in a chair and my wife sits directly across from me in another chair, facing eachother.
While keeping quiet, I let my wife speak.
I sit there and nod my head up and down.
Ocassionally, I say "Yes honey" to affirm that I am listening to her every word.
This exercise gets progressively harder, but continue to complete failure.
Your head may become softer with time but your will and patience will get stronger, as will your neck.
Your significant other will grow a bigger head.
Studies conclude that this workout is good for the heart and will almost guarantee a partner for life.
NOTE: Resist the temptation to move your head from side to side as this will lead to premature failure, resulting in the need to seek a new partner.