So, really what your saying is that you never like to place items that the PC's may have a chance of not finding.
Not at all; I just want the chance of not finding an item to be based on player decisions rather than dumb luck. If there is an element of chance involved, it should have some justification within the established conventions of the fantasy setting.
Mainly, I feel that there needs to be a justification for it rather than just adding chance for the sake of chance. Especially when some potential harm or benefit is riding on that chance. Putting it up to chance strips story-directing power from the players in a context where that power should rightfully be theirs.
If they can't find something, it's not because the dice gods frowned upon them; it's because they lack the capability, the tools, the effort, or the right approach. There are many tricks you can use to prevent easy discovery of every last hidden thing -- one would be the "DM's best friend" mentioned by Greg K. This is a simple rule of thumb that favorable conditions give +2 to a check. If they take 20 for a general search, they get their regular take 20 result. If they take 20 and say they're specifically going to focus on a particular subset of the space of interest (eg, focus on a certain wall in the room, or around the lock on a door), you secretly give them a +2. If they take 20, say they're going to focus on a particular part, and propose an intelligent tactic for testing for a specific feature, you give them +4 (for two separate bonuses). And so forth. So you set the DC above a generic take-20 check result, but within reach of taking 20 with one or two bonuses for specific or creative searching. That way they won't find it if they just say "I take 20 to search the room", but if they notice something specific
I just want dont like the feel of "take 20" equals "find everything I placed in the area without fail"
I think the problem is that you're focusing too much on what it looks like out-of-character and ignoring what's going on in-character. Yes, out of character it's very quick and easy. "I take 20." "OK, you find X." But in-character, they didn't just press some magic "find everything" button, they spent several minutes or even hours closely scrutinizing the space. There's a big difference between normal use of a skill, taking 10, and taking 20. Normal use is when you're under pressure or just trying to move quickly and hope for a lucky break, and you're trusting to chance. Taking 10 is coasting by doing an average job, which you can pull off reliably when you're not under pressure. Taking 20 is being extremely persistent and thorough, trying and retrying until you get it just right. If you take 20 on Escape Artist, you keep wriggling against your bonds until either you slip free or you're confident that these bonds are beyond your capability to escape. If you take 20 on an Open Lock check, you keep working at the lock until you either pop it open or are confident that this lock is beyond your ability to open given your current tools and skill level. If you take 20 on a Use Rope check to rig up a harness, you keep tying, untying, and retying the knots until you're confident you've done the best you can. If you take 20 on a search...well, you see where this is going.
Complaining that taking 20 means they're guaranteed to find hidden objects that are within the limits of their capability to find is like...well, like complaining that if they roll a d20 enough times eventually they'll roll a natural 20. Given enough tries, the law of large numbers states that any outcome with a non-zero probability will eventually occur. You don't want to have things hidden so well that it can't be found no matter how hard they try, so by the same token everything there
can be found if they put forth their absolute best effort. Taking 20 is simply a shorthand for attempting it over and over again until that best effort is made, so you don't have to sit through the tedium of the players rolling search checks for the same 5x5 square over and over and over again until they finally hit the nat-20 they've been waiting for.
Of course, as the DM it's always your prerogative to set the rules of the setting, and if you want to say that some bizarre magical force somehow messes with the laws of probability such that the law of large numbers no longer holds (a truly mind-boggling prospect, really, if you consider the full implications of it), then go for it. But frankly, I have to wonder...
why? I can see why you might want to avoid taking 20 on searches to keep traps relevant, but as I pointed out earlier just because you can find a trap doesn't mean you can disarm or avoid it. You can easily set the DC for disarming a trap above what you can reach by taking 10, so they have to roll to disarm it. Or heck, you could just rule that because of the risk involved with disarming a trap, it always counts as a "stressful situation", so they can't take 10. Taking 20 on search checks does not make traps irrelevant, it just gives the players a chance to brace themselves in case something goes wrong.
Assuming, once again, that they have the opportunity to leisurely take 20 in the first place. Which, really, is more the exception than the rule.
So it really just comes down to hidden doors and items -- things that would mainly serve to benefit the PCs or even add an interesting new twist to the plot. What does it add to the game for there to be something like this that only you will ever know about if the PCs happen to roll poorly?
