Audience management.
Control your audience. Don't let them stand behind you when you do an effect like some creeper. Say something to them.
"You won't be able to see anything from back there." Bring the deck in closer to your stomach. It makes it hard for them to see the deck.
They'll work their way beside of you which is better than the back.
Also if you move your body, your hands, while your doing noticeable moves, it's harder for people to follow the deck and what your secretly doing from behind.
If you don't know they're behind you, and they figure out the method and they're blabbing, I like to say the ever so popular, "Show me" and hand them the deck. They won't be able to do it, then say "Ok, you don't know how to do it then."
One time I was performing, a kid was kneeling, looking up at the deck from underneath it. I was performing for his brothers and his friends and he saw something and I saw his face light up about to explode with a bunch of information.
He looked at me immediately and I just pointed one finger to my lips and said, "Shhh" as I smiled. He went along with it, so I kind of got him on my side. The others didn't pay attention to me because they were still thinking about the trick. Wayne Houchin mentioned this several months ago on his daily updates, which actually worked out in my case.
So there are some things off the top of my head in no particular order. (Sorry I rushed)