Flying away from them is probly a good step. Because your making it unrealalistic. If you can make yourself fly, then you can make the cops go away, right? Its all in your head, you have to know you can do it.

Try spinning within your dream. I haven't had a chance to do it yet, but from what I've read, if you spin yourself around and image somthing, there's a good chance it'll appear. This works with scenery change too. So next time the cops are after you, spin around and image them gone. When you stop, they shouldn't be there.
I'm sure you could search this and get better infromation.