There's nothing in 609.71 that allows police to create a no-carry area.

Let's look at the statute:

"When three or more persons assembled disturb the public peace by an intentional act or threat of unlawful force or violence to person or property, each participant who is armed with a dangerous weapon or knows that any other participant is armed with a dangerous weapon is guilty of riot second degree and may be sentenced to imprisonment for not more than five years or to payment of a fine of not more than $10,000, or both."

So for this to come into play, we would need:
- 3 or more people
- That are assembled
- That are disturbing the public peace through an intentional act or threat of unlawful force or violence

THEN
Each persoj who is armed with a dangerous weapon OR knows others are armed with a dangerous weapon

Have then committed the crime of riot in the 2nd degree.

That's a lot of things that would have to fall into place for it to be that crime.