Haha, blackhawk has the right idea. Go and hire some gangsters to kick the skaters' asses.
But what i would do is just lie to the cops. If they alwys show up at the exact same time, call the cops and say you are witnessing a group of teenagers assulting a women with a weapon, lol. That'll get the cops out to the scene, asap, lol.
Then, when the cops show up and the skaterz deny the charges, you come running along and say you can act as a witness. and since you aren't a teenager and actually an adult, the cops would take you more seriously.