I use a small strike indicator or I use the high stick nymphing technique. I took this off another website re: high stick nymphing: "Once you've found the section of river you are going to tackle, position yourself downstream of the drift your are attempting. Strip out just enough line to cover the water you are drifting, and gently flip your nymph upstream.
As the fly lands and sinks, gently lift your rod tip to remove any slack between yourself and the fly, taking care to keep your fly line out of and off of the water.
Now, move your rod tip downstream at the same speed that your nymph and the current are travelling. As the nymph drifts downstream, it will bounce along the rocks and other debris that sit below the water surface.
If you see a slight pause or anything abnormal happening with the line, give a gentle snap with your rod to set the hook."
That's how I do it.
PC