The Stone would make his transfiguration permanent and thus presumably render them immune to Finite Incantatem. If he doesn’t use the Stone (e.g. in the case of Voldemort, which you are probably referring to), I don’t know of any conventional way to proof against F.I. (Knowing Harry, I’m sure he’d be able to think of some rather unconventional ideas if he sets his mind on it.)
The Stone would make his transfiguration permanent and thus presumably render them immune to Finite Incantatem. If he doesn’t use the Stone (e.g. in the case of Voldemort, which you are probably referring to), I don’t know of any conventional way to proof against F.I. (Knowing Harry, I’m sure he’d be able to think of some rather unconventional ideas if he sets his mind on it.)