Sales rep permissions - lock out ability to change "Lead Source" field?

Sales rep permissions - lock out ability to change "Lead Source" field?

As CEO or VP of Sales, I want to be the only one who can add/edit my "Lead Source" field in a Potentials record. I do now want my Sales Reps to touch this field, but I do want them to be able to add/edit other fields in a Potentials record, and even create new Potentials records.

In User Permissions, I see where I can change user permissions for the ENTIRE Potentials record - but I'm interested in zeroing on on just a SINGLE field in Potentials.

Is this do-able?