So you must always code validation on the server side. Its VERY simple.
1. The Button will always call Page.Validate() when its clicked unless its CausesValidation property is false. This will occur after Page_Load and before your Click post back event method.
2. Your Click post back event method should test Page.IsValid is true prior to saving.
FYI: Professional Validation And More is a replacement to Microsoft's validators designed to overcome its limitations and introduce many things that users have requested. It's client side support includes IE, IE/Mac, Mozilla, FireFox, Netscape 7, Opera 7, and Safari.
--- Peter Blum
Creator of Peter's Data Entry Suite (formerly Professional Validation And More and Peter's Date Package) and Peter's Polling Package