heres an idea,but i you'd have to look for the code to do this
everytime theres a link on the site,and someone clicks it, first it will take you to a new page,in the bottom frame it has the ad,and in this top frame it has a button that says continue to the page you were heading to.now the button that says proceed to the page you're heading to will be disabled until the ad is clicked.
of course the person can just copy and paste the link into a new browser window,but at least theres more exposure to the ads this way,and there will be a higher chance more ads get clicked
or maybe do something where every 10 posts someone makes,they have to click an ad to be able to view or post anymore.