How do I remove a border from a rollover image that has been clicked?

In dreamweaver 8 I am making a menu frame. I have a few ons made by using rollover images. their borders are set to zero and on the page properties I have changed the link setting to no underline. On the CSS styes I have set text decoration to none for a:link, a:hover, a:visited and a:active. When I click on a on, however, I still get a dashed square around it which remains there until I click an other on. How do I get rid of that?