As a fourth level DM one of the things I still haven't mastered is relaying details to players from the abstract imagined world. What I mean is, anything I mention specifically is assumed to be important because I mentioned it. If I'm not careful an offhand detail for atmosphere will set players on long, goose-chase searches. Or, on the other hand, an actual important trigger is easy as pie to find, because, well, again, it had to be mentioned.
This isn't a problem for me with traps because I try to make traps visible anyway. But it relegates secret doors to either easy finds (if I have a specific trigger designed) or impossible finds (search every section of wall you suspect and roll to see if you find something).
I'd love to hear how other DM's negotiate this difficulty, but in the mean time I figured out a kludge of a fix. Make every secret door also a trap if triggered incorrectly.
That way you can have your "There is a moosehead mounted on the wall here" type triggers but players that turn it the wrong way can run into trouble. I'd want the trouble telegraphed the same way I do normal traps-- bloodstains, bones, body parts. And that would mean the existence or (approximate) location of secret doors would not, in fact, be secret any more, but how to pass through them would be.
But then, if you have traps peppered about a dungeon, a trapped secret door might not be obvious. Players seeing it might assume it's just another trap and avoid it altogether. And only normal things that tip off secret doors ("hey, there's a blank spot on the map here!") would send them back to re-check it.
Anyway, here's an example of what I had in mind: a square room has a mosaic running hip-high around all its walls. Each wall has underwater scenes with mermaids, shipwrecks and a single giant clam with a pearl in it. There is a bit of bloody cloth jammed into the crack between floor and wall. Pushing one of the pearls will 1) open a a pit trap below the whole room 2) open a dummy secret door to a dead-end hallway and shut the door behind you in 5 rounds 3) nothing 4) open the real secret door.
I guess that might be more of what people call a "trick," and it certainly makes more work for the DM to put in than a plain vanilla secret door, but it's another possible approach.