Hi,
You should try out Thopmson Park in Licroft, NJ. It is not far from chatham and worth the 1/2 hour trip. It is right off exit 109 of the GSP. The park has a fenced in acre for dogs and is open until the sun goes down. People bring their dogs from all over NJ...it is so worth it for the pooches, and I guarantee that you will have a blast too.
Jennifer (Mother of 'Harry' who frequents the park daily)