Field must contain all letters of the alphabet.
Maximum word length: <n> characters.
Field can contain any word only once.
Sentences must (/not) exceed <n> words.
Word count of every sentence must be a prime number.
Every sentence must be <n> words longer (/shorter) than the previous sentence.
Word count in every sentence must be the same as in post title.
Every sentence must contain a number.
Comment must not contain any (/must contain all) words from the post title.
Post/comment must contain an assertion of who we are at war with, this week.
All of course also for comments.
And yeah, we were always at war with Eastasia ... just to make sure.