Really really late to party but for people like me who read old posts....
If you have wood available maybe a zig zag fence would work. You can work it around trees. Common on New England farms. An example:
https://www.facebook.com/oldsturbridgevillage/posts/z-is-forzig-zag-fence-zig-zag-fences-came-into-popular-usage-primarily-due-to-th/10153091660864979/
