Currently I'm just running adsence ads on my site but I'm thinking of trying a few different ad networks and adding more ad spaces than the 3 that google allow but I don't have a clue on the best practice on doing this. Can anyone give advice or the refer me to somewhere that has guides ect. To keep it simple lets say I were to sign up to 3 different ad agency's each with there own ad codes. They all ask for code for filling unsold inventory. Do I set it up as a daisy chain thought each of the agency's i.e Ad 1 > Ad 2 > Ad 3 > Adsece Or do I use something like Google Admanager to manage it? What happens if Google Ad manager picks Ad agency two but they can't fill the ad do I use the google ad manager code as the backfill code on each ad network? I've really not got a clue and don't know where to start.