over the fence
Adverbial use for actions done across or over a fence, such as looking, talking, or handing something.
I talked with the neighbor over the fence.
noun which may take the genitive case particle 'no'
back-fence
Attributive use, often describing informal neighborly exchanges or gossip that happen across a fence.
I could hear a back-fence conversation.
Compound of 垣根 (fence) + 越し (across, over).