The following mantra can be applied not only for that, but to help improve one's life or to help secure what your heart desire's. More than just a mantra, it requires a surrendering of oneself to the Lord.

Ananyaa shchinta yanto maam
Ye janaah paryupaasatey
Teshaam nityaa bhiyuktaa naam
Yogakshemam Vahaamyaham

To those men who worship Me alone,
thinking of no other, of those ever-united,
(To those men, ever-united in love, who surrender to Me, after having done their best)
I secure what is not already possessed,
and preserve what they already possess.