In this natural experiment, we investigated on-leash and off-leash policies as plausible influences on the behavior of dog-walkers in the City of Calgary, Alberta, Canada. Following policy-mandated public consultations, two of the four parks initially proposed by the City as sites for new off-leash areas retained on-leash designations. Within a year of creating off-leash areas in two parks, we observed more dogwalkers and improved compliance with dog-fouling in one case, but not in the other. Compared to the previous year, we also observed more stationary dog-walkers in both of these parks. Paradoxically, activity levels amongst dog-walkers – including while dogs were off-leash – remained highest for a park that retained an on-leash designation. Off-leash policies in urban parks could have positive as well as negative implications for public health. In addition to off-leash policies, factors that merit consideration regarding dog-walking and dog-fouling include implementation strategies, physical features, socio-demographic characteristics and modifications to park environments.