expression, ichidan verb
look over the fence
Literally to look over a fence or hedge; often used figuratively for peeking into someone else's affairs or envying others.
隣の庭を垣根越しに見てはいけない。
You shouldn't look over the fence into the neighbor's garden.
彼はいつも他人の成功を垣根越
He's always just looking over the fence at other people's success.