town hall question

i have make a map, with locked cam on the hero, but, if the player press backspace, the cam back to the town hall, how i disable this feature?

i need the townhall on map and the locked cam on hero...
i need the town portal item works too...

i'm not at home...so i don't know if this will work...but you could make some trigger like

E: camera moves
A: Move camera back to locked unit