are you farmiliar with a server-side technology?
By using ASP you could build in code that can prevent this from happening. Sorry I can provide samples of this at this moment but if you are going to look at ASP then i would suggest that you post the problem in the ASP forum and i am sure someone can help you.
Dave, yes you can but as Ribeyed indicates, exactly the mechanism depends on what server capabilities you have. If it's only CGI, then it's more difficult than if you have ASP, JSP, PHP type frameworks available.
"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." Brian W. Kernighan