We consider a controlled evolution problem for a set Omega(t) subset of R-d, originally motivated by a model where a dog controls a flock of sheep. Necessary conditions and sufficient conditions are given, in order that the evolution be completely controllable. Similar techniques are then applied to the approximation of a sweeping process. Under suitable assumptions, we prove that there exists a control function such that the corresponding evolution of the set Omega(t) is arbitrarily close to the one determined by the sweeping process.