Fulfillment of complex missions, such as zone watching or multiple target tracking by an UAV can prove very demanding in terms of vehicle ability. A potential way of lessening these demands consists in splitting the initial task into several complementary subtasks. Each subtask can then be completed by one vehicle of a fleet whose cooperation must guarantee the satisfaction of the whole mission. In this paper, zone watching is defined as a cooperative problem where a number of autonomous vehicles must explore a wide area in a limited amount of time. In addition to zone coverage, the dynamical allocation of exit locations is considered. A model predictive control approach is adopted in which the requirements of the mission are specified as cost functions. Simulation results are presented to illustrate the behaviour of the fleet.