Modify Banner Ads for Responsive Design

I have a wordpress site on a multisite network. I use Google DFP for small business for ad delivery... basically adsense code. I need to modify the code for divs to display my ads correctly for different viewports. I'm not worried about adsense terms and conditions because all my ads will be sold locally and not fallback on adsense. Please have experience with responsive sites before you bid on the project. My site has 3 columns in desktop view and collapses down to two on tablets and then one column for mobile view. I currently have my leaderboard ad (728x90) disappear when it reaches the tablet viewport. I need better code for the leaderboard and code that will contain smaller ads (custom size of 300x50) to stay within the particular column. Please view my site http://rheareview (dot) com for illustration. The site is live so this project will require care and caution. I look forward to working with an experienced developer to achieve my goal of serving appropriate sized banner ads according to device/display size. Happy bidding.