This is a tough one to answer. I have an Ameracauna that flies up to my deck rail which is about 8 feet off the ground. She has a nice rail to land on and knows what goodies she might get when she lands.
However, she doesn't go over my 3' high garden fencing like you describe. I used an inexpensive garden fence and attached the bird fencing to the garden fence. It kept my girls out of the part of the garden I didn't want them in for the entire summer. I don't know if it because they can't land on top and then jump down or what, but they don't go over it.
If you are worried about their safety, I am not sure I would use this idea.
Good luck!