Suppose that a fence needs to be protected by k mobile agents with maximum speeds v1, . . . , vk so that each point on the fence is visited by some agent within every duration of a predefined time. The problem is to determine if this requirement can be met, and if so, to design a suitable schedule for the agents. Alternatively, one would like to find a schedule that minimizes the idle time, that is, the longest time interval during which some point is not visited by any agent. The problem was introduced by Czyzowicz et al. (2011). We revisit this problem and discuss several strategies for the cases of open and respectively closed fence.