'Secret' doors are a real pain. If they're actual door objects then they always show up when you hold down the Z key, or when you pass the mouse over them. Even putting a usable placeable in front of them won't always mask them - you might not notice the door when you hold down the Z key, but the cursor still often turns into the door icon even through the placeable in front of it.
If you use a placeable (which can be made usable/non-usable via script) instead of a door, and it leads to rooms in the same area, then you can't easily block the secret rooms from showing up on the area map or minimap (whereas a closed door would). Not without some complex workarounds.
Often the best solution is to use a placeable object instead of a door, and attach a conversation or script that transitions the party to another area. It can start off non-static and non-usable, then be made usable via script when it's been revealed. That way the existence of secret doors and/or rooms can truly remain secret from the player.