1
                                                                    EXHIBIT 4.29

                             SUPPLEMENTAL INDENTURE
                                       OF
                                   GUARANTORS



         THIS SUPPLEMENTAL INDENTURE dated as of December 23, 1999 is delivered
pursuant to Section 10.04 of the Indenture dated as of November 15, 1996 (as
heretofore or hereafter modified and supplemented and in effect from time to
time, the "Indenture") among LAMAR MEDIA CORP., a Delaware corporation,
(formerly Lamar Advertising Company) certain of its subsidiaries ("Guarantors")
and STATE STREET BANK AND TRUST COMPANY, a Massachusetts banking corporation, as
Trustee ("Trustee") (all terms used herein without definition having the
meanings ascribed to them in the Indenture).

         The undersigned hereby agree that:

         1. The undersigned is a Guarantor under the Indenture with all of the
rights and obligations of a Guarantor thereunder.

         2. The undersigned hereby grant, ratify and confirm the guarantee
provided for by Article Ten of the Indenture to guarantee unconditionally,
jointly and severally with the other Guarantors, to each Holder of a Note
authenticated and delivered by the Trustee, and to the Trustee on behalf of such
Holder, the due and punctual payment of the principal of (and premium, if any)
and interest on such Note when and as the same shall become due and payable.

         3. The undersigned hereby represents and warrants that the
representations and warranties set forth in the Indenture, to the extent
relating to the undersigned as Guarantor, are correct on and as of the date
hereof.

         4. All notices, requests and other communications provided for in the
Indenture should be delivered to the undersigned at the address specified in
Section 12.02 of the Indenture.

         5. A counterpart of this Supplemental Indenture may be attached to any
counterpart of the Indenture.

         6. This  Supplemental  Indenture  shall be governed by and construed in
accordance with the laws of the State of New York.


   2


         IN WITNESS WHEREOF, the undersigned have caused this Supplemental
Indenture to be duly executed as of the day and year first above written.

                                        Guarantor:

                                        LAMAR FLORIDA, INC.
                                        a Florida corporation


                                        By:  /s/ Keith A. Istre
                                           -------------------------------
                                             Keith A. Istre
                                             Vice President - Finance and
                                             Chief Financial Office


Attest:


By:  /s/ James R. McIlwain
     -------------------------------
     James R. McIlwain, Secretary

Accepted:

STATE STREET BANK AND TRUST
     COMPANY, as Trustee

By: /s/ ANDREW M. SINASKY
   -------------------------------


Title: Assistant Vice President
      -----------------------------