Should any parts of Marina in San Francisco be avoided more than others?

The Marina in general is a very safe neighborhood, and there aren't any areas in particular that should be avoided from a safety perspective. The only areas I would avoid as a pedestrian are Chestnut St, Union St, and Fillmore around 1:30am when the bars start to empty out. There cans be hoards of bar-goers in the street, and good luck getting a table at any of the late night eateries. Anytime before then, they are very busy, safe, and an excellent neighborhood to explore.