Please don’t give in to the temptation to ‘dumb down’ your cache. Perhaps the difficulty rating needs to be higher than a 3.5 if its really that well hidden. Cacher’s need to pay attention to the rating of a cache, and if its hard, then they need to expect to have to work hard, and possibly even fail at finding it. If people don’t want to work that hard to find a cache, then they should limit the maximum difficulty rating that they choose to go after.
Also, if you make a hard to find cache, and that’s your intention, then expect a sub-average success rate and some complaints, but that’s what a hard cache is all about!