Howling:Weeping angels killable when not being looked at?

The Tenth doctor, in Blink, said that Weeping angels are only stone when you look at them. So aren't they just flesh when you blink or turn your head? Can't flesh be shot and killed(Yes, the doctor doesn't use guns, but River does, and she appears in Time of Angels, Flesh and Stone, and The Angels take Manhattan). Also, can't stone by mined? If this is the case, Weeping angels can't exactly live forever, like we're led to believe 22:04, December 14, 2013 (UTC)