Updated: January 11, 2013
I wouldn't recommend Url Alias (umbraciUrlAlias), since it creates multiple URLs for a single page, making it potentially tricky to trace back. Equally, there's a negative SEO value when you have multiple URLs for the same page.
Still insist on using Url Alias? Then at least add canonical URLs to the meta tags, as shown below.
<link rel="canonical" href="http://yourdomain.com/yourpage" />
Alternatively, you can use uComponents 301 redirect. Not installed uComponents? Install it now :
<notFound assembly="uComponents.Core" type="NotFoundHandlers.SearchFor301MovedPermanently" />