In its on-going defense costs sharing talks with the United States, South Korea will seek a mechanism to prevent Seoul-contributed defense funds from being used in the relocation of U.S. military bases, a government source said Monday. \"In the previous two rounds of talks, South Korea proposed changing the frame of the defense costs sharing system in a way that corresponds to the sound development of the South Korea-U.S. alliance ... and we will continue to focus on that (in the next round,\") the government source said.