If you happened to be walking your dog down Hansastraße in Munich a couple of weeks ago, you could have helped your dog to a free feed of premium pomegranate-based GranataPet dog food, simply by using your smartphone.

Chances are, if you've walked the same dog there since, it's had a particular focus on a single billboard.

In what has to be one of the most ingenious small-budget marketing campaigns ever, German advertising agency, Agenta, devised a billboard that dispensed the dog food into a bowl, whenever anyone checked-in at the billboard on Foursquare. 

The immediate result was that people's friends found out about the promotion through Foursquare and Facebook, but the mid- to long-term result is way better. This is such a cool idea, that people are talking about it everywhere - like here, for example. So maybe 100 dogs got fed, but thousands of people are finding out about GranataPet as a result. Not bad for the cost of a billboard and a dog bowl.

This has only been done in a couple of locations in Munich so far, but with the success of the campaign becoming evident, Agenta Managing Director, Oliver Grage, promises, "Now we are planning to roll out this idea to other cities." But he's being very coy about which ones.

Probably the best way to find out if a GranataPet billboard dog food dispenser is coming to your town is to keep an eye on GranataPet's Facebook page. Better yet, stay tuned to what your favorite brands are up to, because this kind of marketing is only in its infancy. Now the idea is out, it's only a matter of time before it becomes the norm.

Watch it in action - it's like Candid Camera for dogs: