Creating even a 10 mile buffer inside Afghanistan is almost a physical impossibility due to the terrain, the long border, the houses straddling the two borders, the family connections on both sides. Pakistan doesn't have the readily available manpower for that while there is India ready to pounce given any chance, nor Pakistan has the money.
Also, the foolish talks of 'leveling' Afghanistan, as said by some above, is just not possible, even if morality is set aside, short of nuking much of Afghanistan, which we know is not going to happen--and should not happen.
There are really no good options in Afghanistan for Pakistan--and the world. Only long term is a neutral govt, at peace with Pakistan, and with social uplifting of Afghanistan in education, health etc.