There should be a remote wire on the back of the stereo (blue wire) that you tie the remote input on the amp to. This will shut off the amp when the stereo turns off.
Perko switch or inline breaker. You can fix it yourself by running a remote wire to the back of your radio. There should be a blue wire labeled Remote or Amp. Connect the amp to that via small wire and then when the radio turns on, the amp comes on.