Potential has open activity custom field?

I'd like to create a field (boolean) for the Potentials module based on whether or not the potential has an open activity. Is this possible? I've played with it a bit and didn't find a way.

It is my belief that every open potential should have an action item associated with it. I'd like to sort my potentials listing based on whether or not they have an open activity. We need to make sure we follow up on all of them.