You can add FB Open Graph tags to your landing pages and control what is picked up when someone shares the page.
<meta property="og:title" content=""/>
<meta property="og:image" content=""/>
<meta property="og:site_name" content=""/>
<meta property="og:description" content=""/>
I found this site that explains it pretty well.
http://www.quicksprout.com/2013/03/25/social-media-meta-tags-how-to-use-open-graph-and-cards/