ASC and DESC separately from orderby

Question

So I got this to sort my posts and it works great:

<div class="sort">
   Sort by  
     <select onclick="if (this.value) { document.location = this.value; }">  
        <option value="" selected="selected">Latest first</option>  
        <option value="<?php echo $short_page_url; ?>?orderby=date">Oldest first</option>  
        <option value="<?php echo $short_page_url; ?>?orderby=title">Titles A-Z</option>  
     </select>
</div>

But how can I have the order as separate dropdown/links to change between ASC and DESC? So it adds "&order=desc/asc" to the link when there's "?orderby=title/date" present?