Glue for stringed instruments pegs?

I have a cello that keeps slipping whenever I tune it. Its so bad it's to the point where i tune one string but by the time I get to the next one it's already out of tune. I have tried doing the pencil lead thing and that does not work. I talked to someone at a music store about it and he said there is some kind of "glue" (it does not permanantly fix the pegs) that you can drop onto the pegs to make them stick a lot better, they didn't have any at that store so I couldn't get it then and now I forgot what he said it was called. does anyone know what I am talking about?