I once had a double-backed card in my deck - I didn't realise it was in there and so when I got out my cards and handed them to someone to shuffle I heard...
"What the hell is this?!"
There were ooohs all across the room as people thought I'd been rumbled. Thankfully someone interjected and said that all Bikes come with a card like that (they don't) and that it was just an extra card.
Phew!
Of course, the magic that followed was so strong that they don't recall the card now
But that was down to me failing to check my cards beforehand. It seems that your problem stems from your worry that you can't control your audience...would I be right in thinking you are relatively new to magic? The more you perform the more you learn about certain patterns of behaviour - warning signs, things to look out for, so in time you may find that you will be able to detect when someone's about to reach for the cards. The more experience you have the better you learn to handle your audience...kinda learn naturally over a period of time. Or maybe it's a problem with your routining? Sit down, think about it and try and find a way of ensuring that people won't reach for the cards.
Remember, although
you know that you're using gaffed cards your
audience doesn't; if you're worried that someone will reach for the cards then maybe on a subconscious level your audience will pick up on that too, and the trouble makers may reach for the cards...just be confident and hopefully everything will be fine. Treat your cards like normal ones and it's more likely others will.
That said, don't be worried if people mess up the effect and find out you're using double-facers; in time, they will forget about them. It's a trivial thing really, finding out how an effect is done, and not one that would be of any use them remembering.
Hope this helps
