Few months? How about "anAardvarkAndAHippoAreNeverFriends@" easy to remember and almost impossible to brake. Worst case, lets say that attacker actually knows that the password is 6 words with a special character at the end. Lets further assume that the attacker knows that the words are not overly complicated, say from a subset of 5,000, and the special character is one of the 10 that's easy to type on the keyboard. Even than, at the speed of 10 million passwords per second it would take 500 million years (just about) to crack that one, and no need for months of memorization.
Passphrases are not more secure then regular passwords by default, the problem is that a lot of people use phrases that follow simple grammar. Capital first letters of each word, a sentence that is actually valid and no spelling mistakes make it a lot easier to crack then 50 random characters (or 20 random characters).
Passphrases that work are random sequences of words that have spelling mistakes, random capitalization, aren't found in any book/song/poem and preferably mix several languages. The famous "correct horse battery staple" is better then your example, I have memorized 20 random words from 3 languages and use those words in some combination in all my passwords.
