“Cool, then you shouldn’t mind if we search your entire property right now to prove that you don’t still have the thing you are explicitly prohibited from possessing. Or you can show us where you were boating when they were lost and we can charge you for the cost of the search if they aren’t there.”
Start putting these people in jail in large numbers. Make it clear to the rest that they need to surrender their illegal firearms.
“I lost my guns in a tragic boating accident.”
Now what?
“Cool, then you shouldn’t mind if we search your entire property right now to prove that you don’t still have the thing you are explicitly prohibited from possessing. Or you can show us where you were boating when they were lost and we can charge you for the cost of the search if they aren’t there.”