Is there a simple way to generate a un-duplicate string?
<p>I know I can use GUID to generate a unique string, but it's too long. 
Now I only need generate un-duplicate string within an website, how can I do? Thanks!</p>

<p>For example: In the website <a href="http://mathurl.com/" rel="nofollow">http://mathurl.com/</a>, you can generate a permanent URL, such as <a href="http://mathurl.com/75ujy7b" rel="nofollow">http://mathurl.com/75ujy7b</a> and 75ujy7b is very short and un-duplicate.</p>
