Citys and towns usually have a plan to keep gangs from, from gathering, they usually begin with proactive patrols, they direct the units that are n0ormally assigned to a specific areas to patrol

To leave there sectors, and keep the problem areas free of whatever areas  neighbo, this way the area that usually see's one cruiser, see's 3 or 4 more, they keep the gangs moving, if that's not enough, departments assign an officer to stay at the area, for 4 hours, even if it means hiring overtime, or make it a detail, (where officers work off duty for a fee)

It takes time but eventually works, ploice keep all areas clear, by moving the trouble makers, it's very effective, because the problem persons can't get a group to stay long enough.

Good luck

Rocco70