We have several cal courses on sidewalks. They are unlikely to have cars parked (legally or not) on them. They are much safer in terms of traffic. We mark the ends of the course by drilling (star drill & hammer) a 3/4-inch diameter, 1-inch deep hole and fill it with paint. We carry a (hated plastic) drinking straw to blow the dust out of the hole. We have also tried drilling a small pilot hole then pounding a PK nail into it. This requires carrying a battery powered drill. We abandoned this after the first use because we didn't want to add the complexity of remembering to bring a charged drill to each measurement likely to need a new cal course.
As for the joints in the sidewalk, we assume they cause no more inaccuracy than the cracks, potholes, storm drains and assorted bumps encountered in the road along the measured course.