R’ Moshe Cordovero zt”l (the Ramak) was given a special segulah directly from Eliyahu Hanavi, that when one wants to get rid of impure thoughts, he should say the following verse several times until they are gone:
Aish tamid tukad al hamizbayach; lo tichbeh
An eternal fire shall remain burning on the altar; it may not be extinguished. (Leviticus 6:6)
The idea is that each one of us is a miniature Beis Hamikdash, a dwelling place for Hashem’s Shechinah, within which a flame burns eternally and therefore foreign fires such as impure thoughts must be kept out.
Of Course It Only Helps For The One Who Is Guarding His Eyes When He Walks On The Street. As We Say In Kriath Shema 3 Times a Day.