Thanks for the responses. I will definitely get a clip, which will take care of the deck I'm currently using. But I can't get 10 clips, and the problem is that I have many decks and all seem to be warped. Will the card clip correct a deck that's already bowed? So if I have a clip I can put it on any deck and it will become flat again? Or does it need to be used only with a deck right out of the box?
FWIW: My cards are kept in a closet on a shelf, stored upright, with no extremes of heat or humidity at all. I also treat them gently, and keep them in the case. Now, it's not that I need to have scads of decks to practice or perform, but I've bought them in quantity to get price breaks, and it seems like every time I open one, it gets warped, so I go through a lot of decks until I get one that stays flat. I went through my collection of opened decks last night, and even though some were used maybe once or twice, I have about 25(!)warped decks. This is just ridiculous.
Could it be something about storing them?
So far as I can tell, "working them in" doesn't solve it at all. I will do the springing (both directions), some riffle shuffles, etc,(what I've observed experts doing) but it does no good.