friction on the slopes of my terrain problem- 3D

Hi, I was wondering if anyone could tell me how to make my sloped terrain along the outer edges zero friction so the player cannot just jump up a vertical wall and jump off into space.Please. I don't know much about the C# scripting, so i would probably have to cut and paste your code for it to work. or at least get a description of how to code it. Any help greatly appreciated. Thank you.