is cable damascus an ok material to make a guard out of? nor is it too hard and bound to shatter?

High carbon steel including high carbon cable will do what you tell it to in the heat treat process. If you anneal it it will be as soft as it can be. If you harden it it will be as hard as it can be. If you then take it another step and temper you can take as much of the hardness away as you wish all the way down to annealing it. It is not a tough process to learn but it takes more than O am willing to type in this small box. Especially since it is already on here under heat treating stickies. If your eview that lesson and then do some shop testing you will jump way ahead in that one part of blacksmithing. And thanks to those that took the time to put it in writing for the rest of us.