We have investigated a variety of model monolayer films suitable for in situ study by second harmonic generation (SHG). We found that methylene blue (MB), chemisorbed via an intermediate sulfur layer onto nickel and carbon steel substrates, gives SHG signals that are dominated by the MB and are hence suitable to follow film removal during cavitation. No changes in the average orientation of MB were observed for a full monolayer up to a shear stress of 25 Pa, as estimated in previous studies. This indicates that high shear stress does not exert sufficient force on the molecules in the film to change the orientation under flow. Furthermore, we found no removal of the film under shear conditions, and a cavitating jet of liquid was required order to observe removal of the MB from the nickel electrode. This appears to be due to the formation of local pits formed by the cavitating bubbles, resulting in the removal of both the MB and the sulfur monolayer.