Problem
I had a nice photo of a World War I Sopwith Camel and a German Fokker Triplane that I shot at a local Air Show. Fortunately, the photo was against a neutral cloudy background so it was simply a matter of duplicating a few layers and then activating Fluid Mask. To get the very fine strut wires to show I increased the Edge Sensitivity and set the Texture Filter to "Fine". There were a few spots that needed to be gone over with the Complex Mask.  I used the Preview feature a lot to see how it was progressing. I also went over the strut area with the Region Editor to make sure that everything was as it should be.  I found it particularly wonderful that Fluid Mask also enabled me to cut out the fine puffs of exhaust coming from the Sopwith Camel's single cylinder engine.

Solution
When I was satisfied that everything was masked out properly it was a simple matter to cut out the airplanes and then drag the layer with the photo of Death Valley behind it. Then I simply adjusted the levels of each layer to my liking and flattened the image. Voila! A photo of two World War I mortal enemies about to do battle over California's Death Valley.