You know--most seasoned prospectors respect that and won't push the issue. It's usually the newer prospectors that ask questions like that. So, just politely and directly refuse, and explain that you don't want to give up your spot. If they push after that, they're not respecting your privacy and you'll have to decide on what level of discouragement to use after that. Deflecting the topic, or walking away can be very effective.
To show that you're a good guy, you can direct them to an area where they can certainly find gold--everyone appreciates that--but stay silent on your special place.
I get asked the same type of question all the time by people that want to know where I fish to catch the big ones--I politely refuse or just give them a general area--nothing specific.
The previously mentioned ways are the only ways to protect a honey-hole, whether it's a fishing honey-hole or a gold-laden honey hole.
All the best,
Lanny