Not really sure what you mean when you say you want to disconnect two power sources: do you mean two separate power sources connected to two separate loads?
In any case, you could use the classic "locked-out relay" circuit (described in
this post). To disconnect
n power sources, use an
n pole relay (one with that many sets of contacts, one for each power source).
The beauty part of this circuit is that it is fail-safe, which is why it's used in industrial applications (you know, all those switch boxes with the big green and red buttons you see in factories and warehouses). When you reapply power, the circuit will be stone-cold dead until you hit the "start" button again.