Search for contacts who've never been in a marketing campaign

i'm trying to create a search that returns contacts who've never been sent a DM. if i include a criterion based on one of the "campaign response" fields i can see either contacts who have been in a past campaign, or no contacts at all

it seems that any criterion that uses a "campaign response" field returns null if the contact has no responses, which probably makes sense from a sql point of view

anyone know of a better way to approach this without adding custom fields etc?

thanks
ben