Don't allow checking "Neither" if another box is checked

 I am asking a question that I want respondents to be able to answer whether something applies to one city or another, neither or both.

Ideally, I want them to be able to check both Bloomington and Normal, or just Bloomington or Normal, or neither. If any of the City boxes are checked, I don't want people to be able to check Neither. How would I do that?

The easiest way to do this would be to use a single choice field and add an option for "Both".  That way, they can only select one option but have the option for Both: