Ahem, sorry, felt like being a little dramatic.
Have you ever wanted to have your players roll for a skill check but didn’t want them to be tipped off that they failed something? I used to say to roll for your players behind your screen and only tell them if they succeed. Except players can get funny about the GM rolling for them. Players can sometimes feel like they might have passed a roll that the GM failed. It is possible but statistically there should be no difference who rolls for the character. Still, the perception persists and an annoyed player is a player not having fun.
Enter The Box!
Sorry, again with the drama, I gotta get that fixed. So can you have your cake and let the players eat it too? Yes! Here’s a simple solution to the problem that you can use.
Cut a small cardboard box so that it makes a shallow cover, with one side open, just tall enough to allow most dice to slip underneath.
Now when players need to be kept in the dark about the result of their rolls, they get to toss the dice into the BOX OF DOOOM! *cough* *cough* (Man, I gotta call my doctor!)