When the Yetzer Hara strikes hard and we feel suddenly weak, vulnerable and afraid of falling, here are three things a person can do to save themselves:
1) Stop what you are doing and cry out to Hashem. "Hashem, the Yetzer Hara is too strong for me. I need you. I can't do this without you!". These type of Teffilos, coming from the heart work wonders!
2) Make the Ta'avah disgusting in your eyes. Imagine the object of your fantasies as it truly is, flesh and blood, rot and filth. Picture that the skin was being pealed off of the object of your desires, and that you could see what was inside. (For more on this, see tip #11 on this page). This is a powerful technique, and it can also be used effectively when fantasies strike in middle of davening or learning Torah.
3) Make a vow to give yourself a painful penalty if you fall. I recently saw a post somewhere where a person writes how he vowed to give $200 to Tzedaka each time he fell. After spending $400 one week, he stopped cold turkey and never went back to it again. This may sound a bit extreme, but this is a fight for our lives, for our very eternity! Each person should find something painful for themselves that they must do no matter what, if they fall. Maybe jogging 2 miles, or, like in the army, to do 100 push-ups. (For more on making "safe" vows, see here and here).
Remember these three powerful techniques and you will feel strong again!
R' Baruch of Medzibuz explaines that the true meaning of Torah She'Ba'al Peh is that every Jew needs to be Mechadesh (discover) insights in the Torah each day by learning new ways to serve Hashem. And he explains that when we make new fences and guards in areas that we need to strengthen ourselves to uphold the Torah - these are the true "Chiddushim" in Torah, and that is what is meant by "Torah Sh'Ba'al Peh".
As we say "ve'Sen Chelkeinu Betorasecha" - each person has their own Chelek in the Torah. How? Because each person, through his own unique struggles and the fences that he makes for himself because of these struggles, he creates new paths and chiddushim in Hashem's Torah.