I started with New York City itself and ran a Google search for "crime in parks statistics," which brought me here, an article from the Gotham Gazette which states that NYC has only very recently decided to compile crime stats on parks other than Central Park (it's its own precinct, which is why there is crime info available on it). In short, no such information is available as of yet for NYC, nor could I find anything for Chicago, which I decided to try on a whim.
I realize that this isn't a complete answer to your question and I hope that someone takes a crack at discovering whether someone has made a connection between fences around parks and violence towards women. You might actually be able to use the stats concerning Central Park to do that, now that I think about it. Here's a link to Central Park precinct's home page. The crime stats can be accessed there.
I also found this, the website of New Yorkers For Parks, an organization dedicated to promoting and protecting NYC's parks. They also have an interest in protecting parkgoers from crime and were involved in the push to make the NYPD compile crime stats about the parks. Perhaps someone there has made inroads or could help you with more information.