"In this work we introduce a method to stabilize a particular periodic orbit in an initially chaotic system. First, we apply a time delay in feedback which allows us to stabilize several periodic orbits embedded into the chaotic attractor. Then we add harmonic modulation to a system parameter or variable in order to lock one of the periodic states and by such a way to make the system monostable. The method is demonstrated with a Logistic Map and with a CO2 laser operating in a chaotic regime of a Shilnikov type. Also, we study the ability of the most widely used kinds of external harmonic modulation to annihilate an attractor in a bistable system. The comparative analysis of efficiencies to annihilate an undesired attractor of a chaotic Logistic Map with delayed feedback is performed for modulation applied either to a system parameter, to a system variable, or to the feedback strength. The results help to choose the most efficient type of modulation to control chaos and multistability."