magento appends a querystring parameter to CSS and JS

[KatyCouteez]

How Can I appends a querystring parameter to each CSS and JavaScript include in the HTML to clear CSS and JavaScript cache. I have tried \[quote\] \[code\]<action method="addCss"><stylesheet>css/style.css?123</stylesheet></action>\[/code\]\[/quote\]and \[quote\] \[code\]<action method="addItem"><type>skin_css</type><name>css/styles.css?123</name><params/></action>\[/code\]\[/quote\].But each time it returns a the base package like \[quote\] \[code\]http://www.example.com/skin/frontend/base/default/styles.css?123\[/code\]\[/quote\]not my custom theme directory .How to solve this ?