Crazy ex manipulating system as harassment against me and girlfriend -- wat do? (wall-o-text)

Alright so I know this isn't the best venue for legal advice but I'm hoping I'll at least be able to vent some frustrations here.

I used to date a girl, (brilliant, beautiful, etc.), but eventually broke up with her as she had developed a strong dependence on me which was really unhealthy now that we were states away at college.

I've since moved on to my current girlfriend (who I am madly in love with and have been for the 2 years we've been together). my ex didn't take our break up very well...to say the least. In the past 2.5 years she's sent 3 separate police agencies after me claiming I used to beat her, I manipulated her, and that I took advantage of young girls at my job. She tried to befriend my current girlfriend to feed her lies, going so far as to invite her out to lunch so she could tell her the same stories that worked with the cops. All of this is utter horse shit and I tried to play it cool, assuming she would get over it eventually.

Fast forward to my recent spring break. Unfortunately my current girlfriend and ex go to the same college. So when I visited, my ex saw my car. Within 2 days of being there my tires had been popped, a claim was made that I was beating my girlfriend in the parking lot, and another claim was made that I was stalking my ex. So again, another visit with the police. Again, no charges because its again based on the claim that "well someone saw you do it." My girlfriend shows no signs of abuse (just severe annoyance) and we wrap up the day by filing a report about my tires being slashed.

We have at least one report with my ex's name on it as proof that she is at least involved (She claimed that I knew no one at the university except her and that I was stalking her so she feared for her life and wanted me removed from campus), but beyond that the cops refused to name names when ever I asked who accused me.

This doesn't even cover the slander she's spilled online about me to people we used to be mutual friends with.

What the hell can I do to make this harassment stop?

tl;dr ex-gf continuously cries wolf to law agencies in order to harass me and my girlfriend -- and it works. How do I get it to stop?