Police in Denver are laying in stocks of weaponry like pepper spray, assorted projectiles and other equipment to help them should they, as expected, need to disperse protesters this August in the streets outside the Democratic National Convention.

The security preparations, reported by the Rocky Mountain News, suggest that at least some in the city expect a torrid four days. Denver authorities, who received $50 million in federal money to pay for operations due to the convention, will not say what they are spending the money on, although Mayor John Hickenlooper says half the funds will go toward equipment.

Hickenlooper’s reticence is understandable. If security forces reveal how they are spending money to prevent disturbances, those people bent on creating disturbances will have a better idea of how to foil efforts to keep the peace. Municipal authorities say it would be “contrary to the public interest” to give out details of their preparations.

This seems so obvious that it should not need to be stated. But, naturally, the American Civil Liberties Union does not see it that way and is suing for greater disclosure under the Colorado Open Records Act. We’ll let the courts decide what the act does or does not require, but common sense (which is not necessarily the same thing) dictates that the police should not have to reveal operational details in advance.

It will doubtless be argued that the country’s citizenry is entitled to know how it is being policed. This is true. But it is humbug to deny that protesters do not frequently see themselves as pitted against the police, and it is therefore disingenuous to argue that disclosure of security preparations amounts to the minimum transparency required by an open and democratic society.

Modern political protest frequently devolves into a game of cat and mouse. Protesters bent on getting their point(s) across by being as disruptive as possible confer in advance to decide the best way to get around efforts to contain them. Security forces confer in advance — D.C.’s security forces are lending their expertise to Denver and to St. Paul, Minn., in preparation for the conventions — to try and make sure their efforts are not thwarted.

The police try to find out what the protesters are planning, and vice versa. Neither side can be expected to give its plans away. That is what used to be known as unilateral disarmament.