I think any shape that could be viewed from the air would look like a target - I think it should blend in more from the air - and just be powerful when seen up close.
We're talking about rural PA here (no offense to anyone there--I'm captive in suburban PA). It's not like there's much out there, or a great many people who would be affected (as opposed to any city). Terrorists would be able to *drive* up to a memorial out there to destroy it, but it's not like destroying it would scare anyone. Remember, they want to cause terror, and burning a bunch of trees out there won't come anywhere near doing that. I'd be much more concerned about them blowing up one of the gobs of refineries here by Philly.