Enjoyable little puzzle. Very good. Had a look at it about a month ago and had all sorts of ideas that didn't get me anywhere. Then came back to it again this week and within a few minutes had the answer. Funny how that happens sometimes isn't it!
We tried looking for the cache in the evening during the week but when we got there it was too dark to search. Came back this evening and after ten minutes of searching it was starting to get dark again. I started to broaden my search radius (are the coords a little out?) and then found it within a minute.
Took address book and left a marble