Never underestimate the power of heartfelt prayer before G-d. Without G-d's constant assistance, we would not be able to win the battle against this tenacious enemy. Prayers from the heart can be said in the language you know best. To illustrate, here is the translation of a prayer based on an excerpt from the writings of Rabbi Natan, the foremost student of Rebbe Nachman of Breslov, from the book, "Likutei Tefillot:"
"May it be Your will, my G-d and G-d of my fathers, that I merit in Your great mercy and kindness to cleanse my mind of foreign thoughts and false wisdoms, that I not pollute and derange my mind with lusts and sexual fantasies, G-d forbid. And that I not infest my brain with lusts and evil fantasies, and that I not have any unholy thoughts at all. Rather let my thoughts be clean, refined, and pure, without doing anything to cause unholy thoughts to lodge there in the holy chamber of my brain, which is like the Holy of Holies. Give me the strength to overcome all evil thoughts and fantasies that come to confuse my mind, especially the evil thoughts that I have brought upon myself by not guarding my sight, and by looking at illicit images.
"Let me not give room at all in my mind to such polluted thoughts and deeds, which distance me from You with a horrible distance. Have mercy upon me, my G-d, for I know the terrible damage these evil thoughts cause in all of the upper spiritual worlds which are always connected to my mind through the awesome interconnectedness of Your creation, and which sever me from Your holiness, and from the holiness of Israel, the source of my life. You alone know the great and terrible lust which overcomes me, confusing my mind again and again, polluting my very being until my mind is completely filled with evil fantasies. And not only have I not overcome these evil inclinations, but I myself brought them upon myself through my wanton doings, when I knew that this unholy behavior wasn't Your will for Your holy Jewish People. Woe is me for the days that I have wasted in sin."
"Therefore, my G-d, and G-d of my fathers, I come before you with a broken and sorrowful heart, humbling myself before Your Kingship, appealing to Your mercy like a poor man at the gates, that You forgive me in Your abundant kindness, though I be undeserving, and that You bring me from darkness to light, and that you help me from this day forth to sanctify my thoughts. May I be successful in banishing these polluted thoughts from my mind, and avoiding like fire anything that awakens evil fantasies and lust in my heart and my brain. Give me the strength to overcome my evil inclinations, and may my thoughts be always holy and sanctified in Your service. Amen."
("Likutei Tefillot," 1:4)
Translation taken from www.jewishsexuality.com