Chaining to the fence is both illegal & damaging to the paint and plants.

With nice weather upon us and more lanes being rolled out each year, biking has never been quite so popular in the city. However, there are rules to follow and etiquette to abide by. At Cobble Hill Park many bikes are repeatedly locked to the park’s fencing alongside Veranda Place. Though this may seem harmless, it chips the paint on the iron railings and can damage the plantings at the ground level. Volunteers and the Parks department staff work hard to maintain the park’s beautify and repairing the fencing here need not be such a frequent task. Please remember to look for proper bicycle racks and follow these tips on how to lock up securely.
http://gothamist.com/2012/05/15/basic_bike_lock_etiquette_and_safet.php

Want to request additional bicycle racks somewhere? Follow the steps in this DOT link.
http://www.nyc.gov/html/dot/html/bicyclists/cityrack-suggest.shtml