Fencing was nailed with a nail gun. Nail heads are sunk below the face of the vertical boards. Stain collects in these depressions and results in ‘runs’. Puttying is impractical. Any ideas on how to deal with this problem?
The only way to deal with this is to pick-up the runs as they occur with a brush and check a again a little while after applying the stain. You should also spray the stain for better results. You could use a Hudson sprayer designed for stain. You can spray thinner coats of the stain minimizing the runs.