I do as David Trap's last suggestion, Menue: Image - Image Rotation - Arbitrary, after a while you get used to guessing pretty close, I know
In addition to being satified with leveling, (in Ps) I zoom in about half, then grab the photo and drag the horizon down to the Window Frame
Even fussier, slide side to side and make additional 'Arbitrary' decimal point adjustments, eg 0.2 deg anticlock or what is needed ?
Another way is to Prepare on site, take a solid exposure, high ISO, Full appeture, and a few seconds, or what ever is needed; to easily see the horizon, Live View is very handy for this too if not too dark, then adjust camera level accordingly, obviously need to again with different compositions
