A better solution (that I believe is in place [for some people]) is to use some form of electronics to turn off the water (from the pipe) when the level of water (in the bath) gets to a certain level. (I think I was taught about this during a Biomedical Engineering course [at Southampton University]).
It is interesting to think of why this type of system is not implemented more. I suspect it is because the manufacturers of baths do not believe that this will be a problem for most people (and the ones who do have a problem [which cannot be stopped by being slightly more careful {in other terms, those who are disabled}] can seek some form of "after-market" device [solving the problem]).
Angus Higgins