S. C. Gibb holds that some mental events enable physical events to take place by acting as ‘double preventers’ which prevent other mental events from effecting change in the physical domain. She argues that this enables a dualist account of psychophysical interaction consistent with the causal relevance of mental events, their distinctness from physical events, the causal closure of the physical and the exclusion of systematic overdetermination. While accepting the causal powers metaphysic, this paper argues that: Closure is maintained only on the assumption of an implausible pre-ordained harmony between preventing and double-preventing mental events. Distinctness is preserved only at the cost of positing brute unexplained powers of mental and physical events to causally interact with each other. Exclusion is systematically violated in a substantial number of everyday cases. The case for Relevance made by the Double Prevention model is accordingly too weak to sustain a dualist approach to mental causation.