I have a question about your neighbor. You said that your pumped water is affecting your neighbor down steam, and you mention a concern about flooding him during rainy weather. Where did your pond drain prior to pumping?
Your pond looks like a natural depression so I assume it has drained towards your neighbor for many years. How would adding a dam stop your pond from draining the way it currently is?
A larger point I'd like to make, not so much directed at you, but at anyone who builds a pond or dam on their property, is that you (the owner) are liable for damages caused down stream. Just like the gentlemen in the "Bulge in my Dam" thread, if your dam were to fail when you had a full pond behind it, your neighbor would most definitely sue for damages and win. Because a new structure was constructed, and then failed and sent a large flow of water onto his property.
If his home and property lie in the natural drainage and there was nothing I could do to my land to route a high flow away from him, I wouldn't build a dam. You are less likely to be held responsible for natural runoff, but a dam breach is all your liability.
Just my 0.02
Erich
