I actually agree with the comment that a friendly neighbor is a real asset, and an unfriendly neighbor is a real liability.

I completely agree with this as well. And they seem like nice people but I don't want to get in a sticky situation which is why I reached out for advice. They just moved in over the weekend so we don't really know what kind of people they are yet, which makes negotiating with them a little uneasy.

What are they building, anyway?

They are building a fence to surround their yard. But since we already built a fence along the side that borders their yard they want to use it to tie in and build the other 3 sides. Personally, I think it seems really dumb and more problematic to say no and have them build a completely separate fence right up next to ours. Then staining our fence, replacing boards or even replacing that side of the fence if necessary becomes much harder but I don't know what is customary in this situation. And of course that's not even getting into how saying no might affect our potential relationship with them.

The situation is definitely complex which is why I reached out get get advice from others. I want to foster a good relationship with our neighbors but also protect us from issues down the road.