If you won’t be around to vote on December 6th or simply would rather cast your vote early and be done with it then you can do so with an absentee ballot.
See instructions below from the City of Dunwoody website:
A Runoff Election for the Office of Mayor and for City Council Post 4 will be held on Tuesday, December 6, 2011. The candidates for the Office of Mayor are Bob Dallas and Mike Davis. The candidates for City Council Post 4 are Terry Nall and Robert Wittenstein. Any voter who was eligible to vote in the November 8, 2011 General Election is eligible to vote in the December 6, 2011 Runoff Election.
The polls will open on Election Day at 7:00 a.m. and will close at 7:00 p.m. at your designated voter precinct. Voters will be allowed to vote by absentee ballot by making application for an absentee ballot; the reason for voting absentee is not required. The application must be in writing using the application form provided by the State or by written request and may be made in person, by mail, or by fax. The application should be mailed to DeKalb County Voter Registration and Elections Office, 4380 Memorial Drive, Suite 300, Decatur, GA 30032 or faxed to 404-298-4038. The form can be found at www.dunwoodyga.gov or www.sos.georgia.gov/elections. Advanced voting will take place November 28 – December 2, 2011 at the DeKalb County Voter Registration and Elections Office, 4380 Memorial Drive, Suite 300, Decatur, GA 30032.