I'm in a bit of a pickle, lately. I find that, no matter the situation, my players are so amazingly wary of everything I throw at them that they essentially Trapfind/Detect Traps/Detect Magic every speck of dust that floats their way! I'd like to have them cut back on this behavior, as it produces meta-gaming out the wazoo, as well as breaks immersion and generally ticks me off. I've never been the kind of DM who lobs a TPK at them whenever they let their guard down, so I'm not quite sure where this is coming from (besides the fact that they are all too smart for their own good).
Any advice on making them relax for once?
Any number of ways.
1) Talk to them (recommended).
2) Stop using traps and hidden treasure of any kind for several sessions.
3) Give them a time-sensitive mission, then be vastly over-descriptive for a few sessions. They don't go "down the road, and meet a T intersection, where the road branches both East and West". They head down "the road which seems to be made of dark-gray pea-gravel; the left side of the path looks to be just slightly lighter in shade, but still fits the description of 'dark gray'. The road appears to be three inches thick, seems five feet wide, and looks to be lined with two-foot, bright-green grass for five feet, followed by dense bushes going up to human shoulder-height with bright-green three-pointed leaves, which is backed by trees twenty feet tall, with three-inch long pine needles, which block out the light from the sun. This path seems to continue until it appears to reache another road - this one is seemingly of the same makings: it looks to be the same dark-gray pea-gravel; the North side of the cross road looks to be just slightly lighter in shade, but still fits the description of 'dark gray'. The road appears to be three inches thick, seems five feet wide, and looks to be lined with two-foot, bright-green grass for five feet, followed by dense bushes going up to human shoulder-height with bright-green three-pointed leaves, which is backed by trees twenty feet tall, with three-inch long pine needles, which block out the light from the sun" (the repeated description is deliberate). Make sure to use a lot of 'seems to be', 'appears to be', 'looks to be' and similar qualifiers every time you describe anything. Nothing gets a fully concrete 'is'. Keep track of the time and action cost as they check each and every square foot. There are no traps, magical doodads, or anything else of actual note until they come up against an obvious threat (which is exactly as it appears to be, but you keep up the qualifiers). Once the obvious threat is killed, it's obviously carrying obvious treasure - but again, you keep up the 'appears' 'seems' 'looks like' and so on. The mission itself needs to be not overly cumbersome, other than the time limit. Watch them fail due to the time constraints. Repeat until they get the hint.