There is such a thing as a "wall type" hammer and frogspawn that are not easily fragable. Instead of the branching structure normally associated with these corals, the skeleton is more of a continuos "track" of sorts, more akin to an elegance coral. The way to frag such LPS's is to dremmel thru the skeleton from the rear between "mouths" and not break the flesh. Over time the flesh will recede from the point of fracture, and you will have 2 separate colonies.