Gene drives are a powerful technique to reduce the size of a population or to transform it to become less troublesome. Major concerns include accidental escape of a gene drive, which might lead to widespread elimination of a species, or unintended consequences of released individuals, which might include evolution of resistance to an effector gene. Both spatial localization of a gene drive and the ability to reverse a gene drive are desirable mechanisms to increase the safety of drives. A number of such approaches have been proposed in the literature. Using mathematical modelling, we will explore their likely efficacy and discuss critical weaknesses.