Klamath Park, Napa, California
Klamath park is at Trower Avenue next to Highway 29. It is long and narrow with most of it well fenced and the Highway 29 side also lined with mature trees to block the noise. This is not a "dog park" and your human should be kept on a leash. However, if there are not too many people around and you are not worried about your support person running off, take him down to the 1/5 mile walking circle that goes around the most fenced part of the park and they will be fine while you run and play.
Park on Klamath Way. Bring your own plastic bags and a water bowl. There is a fountain but they made it the wrong height. There are benches and tables and even some grills if you are planning a picnic. A good place except summer weekends when people tend to use all the space.