Verify the URL when adding an arbitrary parameter.
Use one of several options, if you add an arbitrary value to the URL:Use canonical URLs
If you can configure your server, you can use rel="canonical" HTTP headers to indicate the canonical URL
for HTML documents and other files.Create custom status code 404 pages
A 404 status code
page is what a user sees when they try to reach a non-existent page on your site (because they've clicked on a broken link,
the page has been deleted, or they've mistyped the URL).Change page URLs with status code 301 redirects
To implement 301 redirect for websites that are hosted on servers running Apache, you'll need access to your server's .htaccess file.
For more information, consult the Apache .htaccess Tutorial
and the Apache URL Rewriting Guide
To properly use the 301 redirect, read our guide
and Google article
Injecting parameters are variables which can be added to the link to an site.