Magento Disable Cache For Particular Block Useing XML.

In my case i have disable cache for footer.

<block type="page/html_footer" name="footer" as="footer" template="page/html/footer.phtml">

    <action method="unsetData"><key>cache_lifetime</key></action>
    <action method="unsetData"><key>cache_tags</key></action>
               
</block>