The first one is easy: The Police agencies encrypt their Tactical channels and leave their dispatch and car-to-car stuff unencrypted. Police still have the ability to mask sensitive operations, the public keeps their "Open" access.
The second answer is a bit more complex -- give the media outlets a radio that is transmit inhibited that has the dispatch channel only on it. I believe that one city (Cincinnati) did that when they moved to P25 a few years ago.
With that said, There's only a trivial space that most radio systems use for encryption these days. In Kenwood radios, it's only 4 numerical digits. While I haven't tried decrypting someone else's NexEdge stuff, a motivated person who wants to hear what's going on, will hear what's going on.