I watched as a child, so not long ago, but because of my age, I must have watched the German dub, or there were subtitles, which may explain my confusion. Some memories are jumbled, so it is hard to recall, but there were aliens in the show, and a girl was crushed by some metal. The dog saved the main characters a lot, who were children. It was a children's show.
There was a K-9 children's series; it would have been broadcast around 2009-2010.
The title character is a robot dog, based on one seen in Doctor Who and The Sarah Jane Adventures. The owner of the the copyright on K-9 allowed the character to be used (sparingly) in those shows, but was not allowed to reference either show in this series.
As I've never seen it, I cannot say if it would have even seemed as if it was post-apocalyptic. It appears to have been set in London in the "near future"; however, there was an element of time travel to the show, which might have resulted in adventures with a post-apocalyptic backdrop.
It was a live action show, with CGI.
I should note that the Wikipedia page lists a number of countries where it was shown, and the channel it was on in each, but that Germany was not included in that list. Not sure if that's just missing information, or if that means it wasn't shown in Germany.
Here's a link to the first episode on YouTube (in English):