Force the use of HTTP

Questions
1

I have a basic textstring which allows people to type in an external link. The problem occurs when they don't put "http://", it breaks the link. How do I force the use of HTTP? Or, if they put HTTP:// leave it out, otherwise put it in for them.

Thanks,

<a href="{$ecmLink}" class="downloadLink" target="_blank">
    <div class="projectTitle">
        <xsl:value-of select="@nodeName"/>
        <!-- small attachment icon -->
        <div class="downloadIcon"><img src="/images/icons/download.png" /></div>
    </div>
</a>
This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/65110-force-the-use-of-http