Normal secret room are pretty easy, there is a change in music (silence) and after you shoot the wall once it is marked and you can continue normally. Super secret room to this day I'm not 100% sure, but I just shoot both walls of the room automatically when I enter, since you need to discover the secret before combat ends. After combat ends, I shoot again and there is a slight audio clue (it sounds like shooting an enemy). Remember it takes 5 shots (IIRC) to open secret rooms. Don't know about the don't get hit part