Different buyer-seller watermarking protocols have been proposed to address preserving the digital rights of both the buyer and the seller. The previously published protocols have faced one or more of the following major common problems which are customer's rights, copy deterrence, unbinding, conspiracy, buyer's participation in the dispute resolution, protocol's practice applicability and man in the middle attack problems. In this paper an effective and secure buyer-seller watermarking protocol is proposed that encapsulates flexible and yet convenient solution to all of the previously mentioned problems. The security of the proposed protocol is based on the security of the public key infrastructure (PKI). The proposed protocol exploits the existence of the trusted certification authority (CA) to solve the conspiracy problem. Furthermore, the proposed protocol solves the unbinding problem based on a novel idea of generating buyer's dual signature of both the purchase order and the buyer?s associated unique watermark.