Property crime was a major concern in Georgian London and previous studies have noted that this fuelled the development of locks, security regimes and policing; by contrast, the role played by dogs in crime prevention has been overlooked. When thinking about eighteenth- and nineteenth-century canines, historians have tended to focus on nuisance strays or spoilt lapdogs, but dogs of all shapes and sizes made a major contribution to the economy by protecting valuable property from thieves. Dramatic evidence from Old Bailey trials and newspaper reports reveals that the bark and bite of watchdogs regularly thwarted burglars and facilitated their arrest. The presence and behaviour of dogs shaped human behaviour and social relations in the city in remarkable ways, as well as influencing debates about crime, social order and the rights of citizens. This culminated with the dog tax debates of 1796 when Parliament was forced to enshrine an Englishman’s right to keep a dog for protection and companionship. This chapter examines canine intelligence and intentionality in action to demonstrate that access to private space, a key battleground in Georgian power relations, was not only controlled by people.