must first of all you times be aware that you have to make a normal police training beforehand and you have no guarantee that you come ever in the dog unit. It is similar with other special branch of the police, including mounted police. After a few years of service, you can apply for this post then.
Therefore you should also be interested in the "normal" police profession bring because it he will first run out.
first for 3 years on the police school without a dog and then continuing with dog. http://www.traumberuf-polizei.de/berufsbild-polizist/hundestaffel/
Do you have enough space, the dog comes to you, after all