So yesterday DS and I took the dogs for a walk around the block. The fencing was still against our fence and garage. When we got back home I noticed the neighbors in question were out in the alley behind their house (well the husband and his elderly MIL were - the MIL lives in a cottage in the back).
So I walked back there and casually asked "Is this fencing yours?". He said "Oh, didn't "Bob" talk to you?" ("Bob" is the neighbor directly behind me. This guy is kiddie corner behind me). He went on to say, "This wall started to slide and "Bob's" fence came down onto our property. He said he would move it and must have forgotten he put it there. I'll remind him to take it to the dump." I said no worries, that I just wanted to make sure it wasn't some random person dumping stuff behind our house.
So, I'm VERY glad I talked to him rather than just putting the fence back on his property, because I guess technically it is "Bob's" fence. And we have a great relationship with Bob. I think he just forgot it was there.
Moral of the story for me is to try and not be passive aggressive when it comes to neighborly relations.
On a side note, the MIL is so cute. I'm standing there with two big dogs and DS is running up and down the alley to catch the dogs' ball, and the MIL invites us all in to see the house since we have never been inside. I told her I'd love to come by sometime without the dogs.