Fragging is taking corals and breaking or cutting them to make smaller pieces to sell/trade/give away to others. There is no such thing as walling, we are referring to a type of frogspawn. As far as I know, there are 2 types. 1st is a branching type that makes new heads by splitting a current head and becoming brancing, kind of like if you splayed your hands open, the tip of each finger would be a new head. These can then be broken off at the base of the branch and sold or traded. The other type is a wall frogspawn. These are an encrusting type where the new frogspawn encrusts on a rock that is touching the current one or the current one and builds more of it's skeleton and new heads form on it. These are usually thicker types and require a different type of fragging where a dremel or bandsaw is needed.