Would you mind answering my question? Thank you in advance.
is "this town rocks" an idiom? is your answer is positive, what does that mean?
1- if that's the sheriff's office, this town rocks.
what about this sentence
2- let's put out heads together.

Question

Answer

Is "this town rocks" an idiom? > No 
"Rocks" as a verb is a slang that means you APPROVE and like that a lot
Example from Net > "Do you like him?" "Yeah, he ​rocks!"

let's put out heads together ( idiom) > to discuss and share ideas with one another to solve something.

Answer

If something rocks then it's cool and interesting.All I got from the first sentence  is that the speaker saw the sherrif's office and found it way better than what he imagined before (maybe he saw the officers doing sth illegal and he thought they are cool guys)...
About the second sentence: putting heads together means sharing ideas to solve a specific problem.
I hope you find the explanations helpful ;)

Answer

By the way in the second sentence "put our heads together" is correct not "put out heads together"... I think it's typing mistake...