The brook across the street from my house is quite narrow in places... 5-6 feet across maybe but deep. Choked with brush on both sides and lots of sweepers.
Traditional up stream fly casting only works on the larger pools. It's just the kind of place most people would avoid.
Some spots are only fishable by sticking your rod tip underwater and letting the fly slip downstream with the current.
A fly with lots of action (like a soft hackle or a woolybugger) is the best way to attract attention.
Do this and you're guaranteed a hit..... maybe not a hook up, but at least a tug.