Try marking your territory with a well-placed pile of feces or via urination. 😉
Definitely take steps to ensure your own safety, but you also might want to seek the strength to be found in numbers. Consider setting up a web page devoted to the issue and then write some letters touting the page to editors of newspapers as well as to local running, cycling, hiking/outdoors clubs and try to build a coalition that can give a stronger voice to the issue through their own particular groups and through a concerted campaign to apply pressure to local officials to improve safety/enforcement on these public lands. Do not expect results overnight, it may take a while before you start seeing the changes you desire. However, trying to go around doing it one dog/owner at a time would doubtlessly take much longer.