Don't.
Never store date information as varchar: store it as DateTime. That way, when you user enters it is can be checked and converted using their culture info as a guide to teh format.
If you store it as a string, then every time you try to use it you have to decide if this:
12/03/05
Is 12th March 2005, or 3rd Dec 2005, or 5th March 2012, or...
Or just plain wrong:
32/01/2014
Late checking is a bad idea, and the very best solution is to change your db now, while it is still small. The later you leave it, the more problems you will get.
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