4 sentences

1. 他背地里说了我不少坏话。

   tā bèi​dì​li shuō le wǒ bù​shǎo huài​huà.

   He said many bad things about me behind my back.

   Source: Dong Chinese Dictionary

2. 那个人阴险狠毒，总是背地里算计别人。

   nà gè rén yīn​xiǎn hěn​dú, zǒng​shì bèi​dì​li suàn​ji bié​ren.

   That person is insidious and ruthless, always plotting against others behind their backs.

   Source: Dong Chinese Dictionary

3. 他被戴了绿帽子，背地里被人笑话是王八。

   tā bèi dài le lǜ mào​zi, bèi​dì​li bèi rén xiào​hua shì wáng​ba.

   He was cheated on and was secretly mocked for being a cuckold.

   Source: Dong Chinese Dictionary

4. 古书中记载，那个奸臣曾多次在背地里贼害忠良。

   gǔ​shū zhōng jì​zǎi, nà​gè jiān​chén céng duō cì zài bèi​dì​li zéi​hài zhōng​liáng.

   Historical records state that the treacherous official had secretly persecuted loyal and upright subjects on many occasions.

   Source: Dong Chinese Dictionary