I think it definately depends on the area. We usually look for a cache for at least an hour before giving up. Then we post the infamous DNF and wait to see if the next guy does the same. If the next post is a find we definately go back. Sometimes though you just know something is wrong. The site sounds like you have to watch for drop-offs and that the view is great from the top and you find yourself in the middle of a cleared off field. You just know not to look very long. Either the coordinates are wrong or you copied or programed something wrong. We then contact the owner and ask him to check. A few times the reply to our inquirery was Opps, so sorry!