引狼入室 -------- set a fox to keep the geese

例句：
A: You'd better keep yourself away from him.
你最好远离他。
B: Thank you for your advice. I know I'll set a fox to keep the geese if I take him for a good friend.
谢谢你的忠告。我知道如果把他当好朋友，那将是引狼入室。

注释：
keep....away from 使......远离