How are players keeping track of which doors a player has uncovered? Once you have discovered a door you do not need to roll again to find it. It seems like a lot to memorize or are we playing this game wrong? Do all four get the knowledge of the door once uncovered?
Assuming you are playing the new WotC version, the rules state
Now all you need is some way to easily reference a specific door. You could try to describe the area it is in, like "Door to east-most level 4 room".
Of course, if you're playing the older "New Dungeon", it wouldn't really be a problem, because in that version you forgot about secret doors as soon as you moved away from them.