Jewels, as in diamonds are non-metalic. gold is different beast
Hopefully diamonds will be like gold in that Twilight Zone episode.
Diamonds were worthless until De Beers paid a marketing agency to make the public think they are valuable.
The loss of value when you as a private citizen sell diamonds is going to hurt a lot compared to gold where you only lose a few percentages to premium spread. With shady diamonds you probably lose 80-90% of the value when you attempt to sell them. If I was hiding wealth it would definitely be gold. Maybe just do multiple sites geographically dispersed so if you lose one it’s not such a big deal
or rubies, or emeralds or any other countless gems that are actually rare (but industrially useless...)
I was speaking towards the method itself is not vulnerable to metal detectors. If you load it up with metal bars, that’s on you.