So, going from the discussion here where I was soundly rebuked and for good reason. I want to give clients unique code snip-its that allow me to change a banner ad without requiring them to FTP anything or change their site. Security is clearly a concern. The ad is code, not an image, as we are testing multiple ad networks. So, to summarize:
-client gets a couple lines of code for each place on their site an ad is placed
-I insert code from ad network (adsense, etc) or our own ad for the location without the client needing to lift a finger
-no security breaches or impact on client site
What would be the best approach to this problem? Minimizing developer time and maximizing security...
One of my clients uses Adjuggler to do exactly what you are talking about. The ads are administered by the agency that sells their ads, they just put a little snippet of Javascript on the site and the ads load dynamically based on the settings and campaigns that the agency sets up.
http://www.adjuggler.com/
The best and quickest solution would be to install an existing advertisement framework that will allow you or your client to add, remove and edit ads through a web interface. There are also a number of CMS suites (drupal, CMSMS, Tiki, etc) that either support ad management natively or have ad modules available. Either solution would require no code be written and allow powerful advertising options.