Display container based on value of another field

I'm designing a property management system and part of it is an application for residency. On the application, the prospective resident is asked to select how they heard about the business. (i.e. Lead Source) This selection is a drop-down list that is populated by a LEADSOURCE entity and the value stored in the application's lead source field is the ID of the selected lead source.

I have another field, "Referred By", directly underneath that I would like to display only if "Current Resident" or "Past Resident" is selcted. I'd like to use the display property of the "Referred By" container to say that if the lead source selected is "Current Resident" or "Past Resident", show the container, otherwise keep it hidden. The problem is that because the application's lead source field is looking for LEADSOURCE identifier, I cannot directly put "Current Resident" or even the id of "Current Resident".

There has to be a simple soultion to this; please help! =D