This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Eric is exactly right. Even if you have client-side guards to prevent this, you still need code not he server to detect and prevent this condition as you can never be certain that the client-side guards will be used.