Create Workflows for inactive leads

Hello

I'm currently mid-build of our Sugar instance and I'm now starting to add the intelligence layers in prep for deployment. I've been asked to create a workflow that would alert a manager when a lead hasn't been worked for 4 weeks. Now, as with all CRM's activities are a separate module to Leads, so whilst a field in the lead record may not have been updated, an activity could well have been completed.

So, my question is, should I add a field to the lead record with some sort of max-date calculation, or even DateDiff. Or, is there a better way of managing this?


Thanks!