Adice to Artists - Political/Parody Art

[star burton]

I recently got commissioned to use a copyrighted character to make political commentary on an issue. I'm relatively certain it falls under parody, and the patron will not be making money off the image. Additionally, the patron has agreed to accept full responsibility for any backlash the image receives. I'm writing up a legal document for them to sign stating all of the above, should I include anything else, and does anyone have any advice on how to word it/etc?