Sneak around (someone's) back

Translation of "sneak around (someone's) back" into Russian

действовать за спиной (кого-то)

He was sneaking around his boss's back to get the promotion.

Он действовал за спиной своего начальника, чтобы получить повышение.

To do something secretly or deceitfully without someone's knowledge, especially in a way that betrays their trust or goes against their wishes.