Split the budget at the county line before you split it by procedure
Metro Nashville and Davidson County run as a consolidated government while the surrounding counties do not, and the buyer changes at the same line the government does.
A single campaign covering the metro will hand its budget to whichever geography clicks cheapest that week. That is almost never the geography with the best patients, because cheap clicks tend to come from the places where intent is thinnest.
Give each county its own campaign and its own budget so that neither can borrow from the other. You then get to see, without arithmetic, what a Williamson County patient costs against a Rutherford County patient, and you can move money on purpose.
Set location targeting to people present in the area rather than people present or interested in it. The interest setting will show your ads to someone in another state reading about Broadway, and dental demand does not travel that way.
Name the places you will not serve and exclude them on day one. If nobody is driving from Mount Juliet to your Bellevue office, stop paying for that click before it becomes a habit.