silly question re: stopping mid-row and keeping yarn on.

[hedgewick]

Ok, hope I don't sound like an idiot. What do you all do to keep your yarn from coming off the needles if you have to stop mid-row and put your stuff away? Or for that matter, even if your row is complete? I seem to think that there is somthing out there to stick on your points so that the yarn doesn't escape but I can't for the life of me find them to buy. Help!