Well, again, what do you do when someone shows up with a weapon?

If you don't want guns in the church, then don't call the police, because they will certainly bring guns.

How about a sign that says this, on every church:

"By order of the Cardinal Archbishop of Chicago, you are hereby on notice: in the event someone enters this property and carries out violence, you should not:

1) Bring, let alone use, any weapon to defend yourself or others.
2) Call the police, because their weapons are not permitted.
3) Expect any help that requires the use of a deadly weapon.

Good luck!"