Morris Arboretum is a spot that I recommend a lot to people who are looking for a spot that isnt downtown Philly but has lots of outdoor space to work with.  Just on the outskirts of Philly, Morris offers a perfect layout for engagements session but its also a great wedding venue too.  Either way there is usually more locations for photos than time to shoot at all of them so you wont have to worry about that.  No permits are required but personally I ask couple to pay for admission for myself.