Shaykh Yasir Qadhi talks about a Du'a that can be used to ask Allah, to keep you firm.
"Our Lord, let not our hearts deviate after You have guided us and grant us from Yourself mercy. Indeed, You are the Bestower."
[Surah Ale Imran , Verse 8]
This dua is very important to be forever and firmly guided and not to be misguided once we have achieved Hidayah.
The Prophet (SAW) always made Dua to Allah to never be misguided and to stand firm on the path of Hidayah. So our stand should be even firmer on this Dua.