We live in a semi, neighbours have an extension right on the boundary so their house goes further back than ours. The first part of our garden has their extension wall as the boundary.
When we moved in there was a waste pipe from their extension that bent down before going underground and was definetly on our property. We did casually mention that at some point we will also be extending and that this would be in the way. No problem said neighbour, they're remodelling the kitchen soon and will get rid of pipe.
So 2 years later they've remodelled the kitchen. Pipe was disconnected, though DH had to remove it as they just left it in situ. Anyway they've replaced it with a kitchen fan/vent outlet. Which is a little bit stupid as we can build right up to their wall.
Anyway this vent thing has little flaps which open when the fan is on. Flaps probably do extend into our garden but only by about 1" and not exactly causing a problem at the minute. However DH is fed up with their cooking smells and has taken to putting a garden cane against it to stop it "opening". I keep moving the cane. But DH says he's going to go round and moan at the neighbours......