Sugar loaf mountain on rte 270 could offer both panoramic views of sunrise or set, and has a nice flat space at the top, along with a spooky sort of stone watch hut for one of the mountain's sides, there is parking somewhat toward the top and the peak approach is doable by 3 routes. I recommend it to anyone, but it might be great for the locale of a fight scene.
Also, you could consider great falls park at the potomac river and RTE 495(clickety)
. There are a few foot bridges with stunning scenery on either side, and I believe both are out of sight of the other.
The trouble is that it may be difficult having undisputed access to these spaces (sugar loaf might be much easier post season)
Some sugarloaf images
fort (watch house)
top of fort
steps at the fort
there are more images at this link: Sugar Loaf Mountain gallery(click)
. By the way, sugar loaf is only 42 miles from downtown arlington; exit 22 RTE 109 off of RTE 270
hopefully not too many people will mind how hard i am geeking out on this.