Magnetism and superconductivity compete and coexist in many of the high temperature superconductors, and the newly discovered iron arsenides are no exception. Muon-spin rotation is ideal for probing the physics of this phenomenon and this proposal is just such a study for some newly synthesized families of these compounds. We have identified two series: Sr1-xNaxFe2As2 and doped Sr2VO3FeAs [we have substituted both the isovalent Ca onto the Sr site, and (separately) the aliovalent Mg onto the V site]. Our samples have been synthesized and characterized in Oxford and also studied using synchrotron x-rays and neutrons. Muons are extremely effective for mapping out the phase diagrams of these iron arsenide families and revealing the nature of the magnetic and superconducting phases and how these can be controlled using doping.