  The question of whether to attempt deflections during planetary defence
emergencies has been subject to considerable decision-making analysis (Schmidt
2018; SMPAG Ad-Hoc Working Group on Legal Issues 2020). Hypothetical situations
usually involve a newly discovered asteroid with a high impact probability on a
set timescale. This paper addresses two further complexities: (1) limiting
missions to an asteroid due to the risk of a human-caused Earth impact; and (2)
active management of asteroids to place them in "safe harbours", even when
impact risks are otherwise below "decision to act" thresholds. We use Apophis
as a case study, and address the two complexities in turn.
