Limit access to the property. Limit the number of entrances and exits. If possible, block the drive around and behind the church to limit individuals from parking behind the church. Insure that the church complex exterior has proper lighting. Sneaky vandals don't like the exposure of light.
Criminal activity flourishes in dimly lighted areas.
They probably won't stay. If certain areas are not to be used during the service, they should be locked, therefore, denying vandals a place to hide. Limit access to groundskeeper tools. Ladders left outside increase the likelihood of both burglary and vandalism. If you need a ladder at your church, store it inside a locked room, or build a small outbuilding for these products.