Dua When fearing the enemy

اللَّهُمَّ إِنَّا نَجْعَلُكَ فِي نُحُورِهِمْ وَنَعُوذُ بِكَ مِنْ شُرُورِهِمْ

"O Allah, we make you the turner of the (enemies) chest (heart) and seek refuge in You from their evils". (Abu Dawood)