They set off, two men out in front as scouts, two behind in case of any attack from the rear.

他们出发了，两人在前作为侦察员，两人殿后以防后方攻击。

《柯林斯英汉双解大词典》

If you know someone is coming up behind you to attack, turn toward the person with your hands up in front of your body and loudly say "stop" before walking away.

如果你知道有人从你后面走过来要攻击你，把手举到身前，转身大声说“停”，然后走开。

youdao

As Israel conducts a big civil-defense drill this week, Syria will hold an unprecedented exercise to test the readiness of the home front for a possible Israeli attack.

就在以色列这个星期进行大规模民防演习的时候，叙利亚也将展开一场空前的演习，检验在以色列发动袭击的情况下叙利亚的后方是否作好了准备。

youdao

Armed escorts lead the way along the former front lines, and attack helicopters keep watch overhead.

CNN: Troops in Bosnia

Patricia Marquis, director of the RCN South East region, described it as "a direct attack on front-line clinical services".

BBC: Guernsey's Princess Elizabeth Hospital

Mr Penny said the fatal attack, in front of passengers, "lasted in the region of 45 seconds".

BBC: Gang members get life terms for East Dulwich bus murder