We are witnessing an exponential increase in IoT applications resting on global mobility of objects. Mobility requires moreover roaming to allow any device to move from one IoT network operator to another. The solutions proposed in the literature are however neither scalable nor secure. The consequences for devices' owners with large fleets of roaming objects may seriously impact the economic benefits of the involved services. We tackle these issues starting from IoTRoam a compliant open-source implementation of the LoRaWAN roaming architecture. This one based on regular DNS resolutions suffers from the limitations indicated above. We propose to modify IoTRoam by introducing a new entity called DNS Broker responsible for orchestrating in a decentralised fashion roaming between different operators using private and secure DNS resolutions. We experimentally show the feasibility of our approach. A preliminary performance evaluation of our implemented architecture shows equal performances for a more flexible, scalable and secure architecture.