Right now the only targeting that's available is by gender/age/keyword/etc. or you can target specifically fans of your page. So, there is now way for your competitors to specifically target people who visit or are fans of your page, but there's also no way to limit which ads show up when people are viewing your page.
Not yet
Ellie Mirman 2 years 38 weeks 3 days 7 hours ago
I don't believe this is an option... yet.
Right now the only targeting that's available is by gender/age/keyword/etc. or you can target specifically fans of your page. So, there is now way for your competitors to specifically target people who visit or are fans of your page, but there's also no way to limit which ads show up when people are viewing your page.