如何仅更新页面的特定部分？

I am using two update panels in my aspx page. My page also contains other controls most of them are text boxes. some text boxes using ajaxwater mark extender. My problem is when the portion of the panels is updated the watermark textbox also updated. How can I preven this to happen? My page is like ....some other controls and thenI am using two update panels in my aspx page. M