书面语：我做你的后盾。 日常正式语：我支持你。 网络流行语：我顶你；我挺你。

There is no direct translation of this English expression into an idiomatic equivalent in Chinese. The best one can do is to "transcribe" the idea, saying something like "不要擔心，我會罩著你，做你的後盾” - "Don't worry, I will cover you and be your shield from behind."

我支持你。 我挺你。

thank you, miss chen!

Chinese mag say 不管怎么样，我都支持你！