Simple: don't do it.
Stop storing dates in databases as strings. You can't properly do any testing or comparisons between strings containing dates, unless you have stored them in a very specific format:
(with or without the slashes). If you store them in any other data format, you comparisons will always involve changing from a string to an actual date every time you try to use them. And to add to that problme, you have to convert them to a date format in order to present them to the user in his preferred format.
So store them as a DateTime (or a DateTime2, whichever) and you cna compare them without problems, and display them in whatever format your user prefers.