a-RuCl3 is a honeycomb lattice system which is thought to be close to a spin liquid state. The layers are weakly coupled and therefore the system is susceptible to stacking faults (though there are conflicting reports of the nature of these stacking faults). We have previously studied a powder sample of a-RuCl3 with muons and found two precession signals that are associated with two different transition temperatures. This proposal is to repeat the experiment but with a single crystal sample which is known to exhibit different magnetic properties and a lower transition temperature. It is thought that the number of stacking faults can be controlled by stress so we will also attempt to measure crystals in both the pristine state and after having applied mechanical stress.