If one simply remembers that they must refuse all requests by the police, other than those they must adhere to - while always being polite - this will almost certainly not happen to you.
There is an ACLU video on this. One fun part is when the guy is asked to get out of the car, he gets out and locks it, with his passengers inside. The cop does all sorts of “if you were innocent, you’d let me” arguments regarding the guy saying no to his requests.
And this is the hard part: Politely refusing. The only thing I’ll do is answer simple questions. If they get complicated I let them know I really don’t have time for it - nicely - and since I’ve done nothing wrong I’d really like to get where I’m going before I’m late.
Oh.
I see now.
You are concerned about green being found in the car.
All the cops have to do to get probable cause to tear apart your vehicle w/o your permission is get their dog to come up and bark at your car. The cop will say that the dog is reacting to drugs even if the cop has to pull on the leash or pull out a tasty treat.
All they have to do to request a K9 check is to state on the report that you looked nervous and your car smelled like drugs. If you were wearing sunglasses and had an air freshener, even better.
All they need to do to keep your cash is test it for minute traces of cocaine or cannabis. You’re a drug dealer until proven otherwise.
If you must transport physical stores of value, consider rare stamps, rare documents, baseball cards, small antiques etc. (but not one of a kind items). Otherwise, you could melt gold into a common object or structural component and paint it or re-form some platinum (it looks like stainless steel)
Using secret compartments in vehicles is still legal in most states, but some like Ohio have made it illegal. Cops also might even use ultrasound to look for modified compartments.