The M-44 ejector (ejector) is a more target-specific means of lethal control of red foxes (Vulpes vulpes) than conventional meat baits, which may expose a wide range of non-target species to the bait toxicant. Owing to the threshold pulling force required to activate the ejector, undesired exposure is eliminated in many smaller animals that cannot generate this force. However, the spotted-tailed quoll (Dasyurus maculatus) and the Tasmanian devil (Sarcophilus harrisii) remain potential non-target species because of their larger size. In this study, we report on the development of a collar that excludes devils and quolls by exploiting differences in their head morphology relative to that of red foxes. The collar potentially prevents bait removal by larger non-target species, while still allowing all adult foxes access to the bait to trigger the ejector mechanism. Spotted-tailed quolls small enough to access the bait are theoretically too small to trigger the ejector mechanism set at a threshold pulling force of 2.7 kg.