Custom field: URL

I would like to use a custom field to produce an URL.
Without writing the HTML-code (a href…).
I wonder if this is possible.

I tried a bit on this page with
$lcp_display_output .= '<a href="'.$this->get_custom_fields($single).'>URL</a>';

but it seems that the custom field immediately breaks the code, interrupting with
<div class=" and
lcp_customfield"=""

I hope you know a way to get this accomplished. Otherwise, i will just have to fill the
custom fields with the HTML code (a href etc)

The page I need help with: [log in to see the link]