Stop autofill (not password) in safari?

I'm entering data on a website (repetitively). I don't want safari to get cute and think it knows what I want. I've gone in to autofill preferences and removed that one site, but after 10-15 entries on that same site, safari starts trying to autofill. Wouldn't be a problem except the fields are conditional and I get a chained error message that the data doesn't fit the parameters (date must fall after first entered date).

How do I PERMANENTLY disable autofill of information on a website within safari?