Hold your breath!
I've been thinking a lot about it lately and I realized that looking at inappropriate things is just like smoking - either first hand or second hand - and we should approach it the same way. Let me explain. Every time I walk around someone who smokes, I try to make sure I don't inhale any smoke because I realize that any amount of smoke is dangerous and can kill me. Even though a little smoke here and there seems quite innocuous, it remains permanently in my lungs and eventually can add up to cause tremendous harm.
The same is true with improper sights (and thoughts, for that matter). A little peek might seem harmless, but it leaves a permanent mark on my neshama (that is, of course, if I don't do teshuva), and every bit adds up to cause more and more harm until... I don't need to finish that statement.
Therefore, the same way one would be careful to avoid smoke at any cost, and hold your breath when you see someone smoking, the same is true with an inappropriate sight. Every sight can and will kill you. If you realize the danger of every little inappropriate image, hopefully, you can fight the urge a little better.