Similarly, I use lyrics of songs I know well enough to be able to sing the words correctly, but are obscure enough that most people won't know them. Jut use the first letter of each word, and if you forget, you can hum along with it while typing.
As an example, the chorus of the classic CCR song 'Have you ever seen the rain' (don't use this one) will give you a easy to remember 15 char password: Iwkhyestrcdoasd. And if you forget its easy to make a simple hint (something like 'Fogerty').
My advice, don't use the chorus - a 2nd or third verse you remember is better (and often longer). And google the lyrics before you make the password, just to check that you've been singing the right words all these years.