mousemove but only trigger once if in an element
<p>How can I improve the following so that I only trigger an event once per element?</p>

<p><a href="http://jsfiddle.net/victorfoster/Q3JmZ/1/" rel="nofollow">http://jsfiddle.net/victorfoster/Q3JmZ/1/</a></p>

<p>I would like a square to only be toggled once when dragging over it, not multiple times.</p>
