How do I get additional banner-ads on pages without sidebars in Zen Cart?

I am trying to ad a banner ad to the left side of the footer so I have something like this:

[ banner ] [ footer information ]

This is the code that was in the basic banner module:

<div class="content">
    <?php
    $content = '';
    // if no active banner in the specified banner group then the box will not show
    if ($banner = zen_banner_exists('dynamic', $banner_box_group)) {
        $content .= '<div id="' . str_replace('_', '-', $box_id . 'Content') . '" class="sideBoxContent centeredContent">';
            $content .= zen_disp开发者_运维知识库lay_banner('static', $banner);
    $content .= '</div>';
    }
    echo $content;
?>
</div>

Which works fine on the home page (it displays an ad like I expect it to). It does not however display any ads on some of the other pages. I expect that it is something to do with the sidebar as it is turned off on the pages that the ads choose not to display. What am I missing?

---

Ah, it turns out that

$banner_box_group

needs to be a string of banner groups separated by colons, so something like:

'BannersAll:Sidebox-Banners'