This paper investigates practices of border formation through an analysis of Australia’s quarantine processes. We use the work of the Australian Quarantine and Inspection Service (AQIS), through the Northern Australia Quarantine Strategy (NAQS), to interrogate the ways in which borders are made and remade in daily life. By exploring quotidian practices of quarantine we argue that borders are the sites of complex and fluid relationships that are constantly being renegotiated as multiple active agents cohabit, contest, belong, and exclude. We find that quarantine borders are constantly being (re)made by forces outside NAQS’s control, including through the practices of Yolngu Indigenous land-management staff and rangers, individual local residents, and diverse nonhumans. Borders are revealed as active spaces produced in multiple locations at multiple scales. They are underpinned by diverse ontologies and are always more-than-human. This challenges the overly simplified view evoked within AQIS’s public awareness material and the prevailing national discourse of defence, invasion, and fear. Through attention to quotidian practices of border making, different ways of understanding borderland geographies emerge.