4 sentences

1. 他不慎从马背上跌落。

   tā bù​shèn cóng mǎ​bèi shàng diē​luò.

   He accidentally fell off his horse.

   Source: Dong Chinese Dictionary

2. 他把马鞍固定在马背上。

   tā bǎ mǎ'ān gù​dìng zài mǎ​bèi shàng.

   He fixed the saddle onto the horse's back.

   Source: Dong Chinese Dictionary

3. 骑手在马背上放好马鞍。

   qí​shǒu zài mǎ​bèi shàng fàng hǎo mǎ'ān.

   The rider placed the saddle on the horse's back.

   Source: Dong Chinese Dictionary

4. 过去九年，我都是在马背上度过的。

   guò​qù jiǔ nián, wǒ dōu shì zài mǎ​bèi shàng dù​guò de.

   I've been on horseback for the past nine years.

   Source: OpenSubtitles