Possible Clues:

• Police state's ending small patch of growth
• Manage to conceal spades in thicket
• Dense thicket, rumoured to be associated with thieves in romans policiers
• Thicket of bushes
• Savannah growth
• Manage to conceal source of sound in some trees
• Manage to get round southern wood
• Dense growth of shrubs or trees
• That would, by the sound of it, be the police
• Manage to enclose small thicket