http://www.geochecker.com/
With the increasing cost of fuel, getting the co-ords wrong on puzzle caches/etc can be expensive.
You can email/phone the owner for confirmation, but if you are like us, we are more often out and about (and out of mobile range) than in.
Quotes from the web site
Am thinking about using this tool for some of my caches.It's completely free
Usage for Cache Owner
If you are a puzzle cache owner, and you would like to use this site to let solvers check their solutions, it's very easy. Simply enter the cache name, waypoint, and GPS coordinates to be checked in the boxes below and submit the data. The next page will present you with the HTML code for a hyperlink to be inserted into the cache description. It's important to use the complete link for the checker to work properly. It's also a good idea to make sure that the link works properly and that the correct coordinates return a positive result. (This tool assumes coordinates are in the typical WGS84 datum used by Geocaching.com.) As the cache owner, you will be able to track how many solutions are attempted - both good and bad. This is a great way to make sure your puzzle is not proving too easy or too hard.
[ + ] Usage for Puzzle Solver
On various puzzle caches, you will find a link to this site, with some encoded information. You simply follow the link to this site and enter the coordinates and submit the form. You will then be told if the coordinates entered match the code in the link.
If you don't find a link to this site on your puzzle nemesis, contact the cache owner and suggest this site. But don't bother with the form below - you'll just end up checking your own solutions! Naturally your own answers would agree with themselves... that really won't help, will it?
Once you have a correct solution, we even make it easier by providing a Google Maps overview of the cache location. How much easier can it get?
[ + ] Abuse Prevention and Privacy Policy
When you check cache coordinates, you will need to enter a five-digit numeric code. This helps to prevent automated solution attempts. Also, you are limited to 10 attempts in any 10 minute span - this should be enough to try a few solutions without interruption, but should prevent attempts to attack cache coordinates via scripting. For this reason, your IP address and what actions you take are logged, but coordinates are NOT logged. Log files are periodically recycled and are not permanently stored. You can read more about GeoChecker's security in the frequently asked questions.
Please note that because coordinates are not logged, and because of the one-way hash, it is IMPOSSIBLE to recover coordinates from this tool. Please do not ask - it simply cannot be done. If you lose the encoded link, simply create it again!
Others might find it useful too.
Kevin
Without a list of multi's that I must go back and find next time (or maybe the next time after the next time, etc.) much of the REAL fun of geocaching would be missing. I need the occasional cache that I cannot find on the first or second .... go to keep the annoyance factor of caching UP and the satisfaction of finding said caches HIGH 
