<PAGE>
                                                                   EXHIBIT 10.40
                                JOINDER AGREEMENT

      JOINDER AGREEMENT dated as of June 9, 2003, by the undersigned, Stokely Ad
Agency, L.L.C., (the "Additional Subsidiary Guarantor"), in favor of JP Morgan
Chase Bank, as administrative agent for the Lenders party to the Credit
Agreement referred to below (in such capacity, together with its successors in
such capacity, the "Administrative Agent").

      Lamar Media Corp. (formerly Lamar Advertising Company), a Delaware
corporation (the "Borrower"), and certain of its subsidiaries (collectively, the
"Existing Subsidiary Guarantors" and, together with the Borrower, the "Securing
Parties") are parties to a Credit Agreement dated March 7, 2003 (as modified and
supplemented and in effect from time to time, the "Credit Agreement", providing,
subject to the terms and conditions thereof, for extensions of credit (by means
of loans and letters of credit) to be made by the lenders therein (collectively,
together with any entity that becomes a "Lender" party to the Credit Agreement
after the date hereof as provided therein, the "Lenders" and, together with
Administrative Agent and any successors or assigns of any of the foregoing, the
"Secured Parties") to the Borrower in an aggregate principal or face amount not
exceeding $1,250,000,000 (which, in the circumstances contemplated by Section
2.01(d) thereof, may be increased to $1,750,000,000). In addition, the Borrower
may from time to time be obligated to one or more of the Lenders under the
Credit Agreement in respect of one or more Swap Agreements under and as defined
in the Credit Agreement (collectively, the "Swap Agreements").

      In connection with the Credit Agreement, the Borrower, the Existing
Subsidiary Guarantors and the Administrative Agent are parties to the Pledge
Agreement dated March 7, 2003 (the "Pledge Agreement") pursuant to which the
Securing Parties have, inter alia, granted a security interest in the Collateral
(as defined in the Pledge Agreement) as collateral security for the Secured
Obligations (as so defined). Terms defined in the Pledge Agreement are used
herein as defined therein.

      To induce the Secured Parties to enter into the Credit Agreement, and to
extend credit thereunder and to extend credit to the Borrower under Hedging
Agreements, and for other good and valuable consideration the receipt and
sufficiency of which are hereby acknowledged, the Additional Subsidiary
Guarantor has agreed to become a party to the Credit Agreement and the Pledge
Agreement as a "Subsidiary Guarantor" thereunder, and to pledge and grant a
security interest in the Collateral (as defined in the Pledge Agreement).



                                       1
<PAGE>
      Accordingly, the parties hereto agree as follows:

      Section 1. Definitions. Terms defined in the Credit Agreement are used
herein as defined therein.


      Section 2. Joinder to Agreements. Effective upon the execution and
delivery hereof, the Additional Subsidiary Guarantor hereby agrees that it shall
become a "Subsidiary Guarantor" under and for all purposes of the Credit
Agreement and the Pledge Agreement with all the rights and obligations of a
Subsidiary Guarantor thereunder. Without limiting the generality of the
foregoing, the Additional Subsidiary Guarantor hereby:

            (i) jointly and severally with the other Subsidiary Guarantors party
      to the Credit Agreement guarantees to each Secured Party and their
      respective successors and assigns the prompt payment in full when due
      (whether at stated maturity, by acceleration or otherwise) of all
      Guaranteed Obligations in the same manner and to the same extent as is
      provided in Article III of the Credit Agreement;

            (ii) pledges and grants the security interests in all right, title
      and interest of the Additional Subsidiary Guarantor in all Collateral (as
      defined in the Pledge Agreement) now owned or hereafter acquired by the
      Additional Subsidiary Guarantor and whether now existing or hereafter
      coming into existence provided for by Article III of the Pledge Agreement
      as collateral security for the Secured Obligations and agrees that Annex 1
      thereof shall be supplemented as provided in Appendix A hereto;

            (iii) makes the representations and warranties set forth in Article
      IV of the Credit Agreement and in Article II of the Pledge Agreement, to
      the extent relating to the Additional Subsidiary Guarantor or to the
      Pledged Equity evidenced by the certificates, if any, identified in
      Appendix A hereto; and

            (iv) submits to the jurisdiction of the courts, and waives jury
      trial, as provided in Sections 10.09 and 10.10 of the Credit Agreement.

      The Additional Subsidiary Guarantor hereby instructs its counsel to
deliver the opinions referred to in Section 6.10(a)(iii) of the Credit Agreement
to the Secured Parties.



                                       2
<PAGE>
      IN WITNESS WHEREOF, the Additional Subsidiary Guarantor has caused this
Joinder Agreement to be duly executed and delivered as of the day and year first
above written.

                                           Stokely Ad Agency, L.L.C.,
                                           an Oklahoma limited liability company

                                           By: Lamar Central Outdoor, Inc.,
                                                            Its: Managing Member

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

Attested:

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

Accepted and agreed:

JP MORGAN CHASE BANK,
  as Administrative Agent

By: /s/ Joan M. Fitzgibbon
    --------------------------------------
   Title: Managing Director



                                       3
<PAGE>
The undersigned hereby respectively pledges and grants a security interest in
the Pledged Equity and evidenced by the certificate listed in Appendix A hereto
and agrees that Annex 1 of the above-referenced Pledge Agreement is hereby
supplemented by adding thereto the information listed on Appendix A.

Lamar Central Outdoor, Inc., Issuee

By: /s/ Keith A. Istre
    ----------------------------------------
        Keith A. Istre
Title:  Vice President-Finance



                                       4
<PAGE>
Supplement to Annex 1
                                                 Appendix A to Joinder Agreement
<TABLE>
<CAPTION>

             Pledgor Ownership                  Issuer              No. Shares      Cert. No.      %

<S>                                    <C>                          <C>             <C>           <C>
                                       Stokely Ad Agency, L.L.C.
        Lamar Central Outdoor, Inc.                                 1000 units          2         100
</TABLE>

                                       5