Don't Stop The People, Outlaw The Dinghies

No dinghies, no immigrants.

The French, or the EU, pass a law that requires all dinghies - which will be very broadly defined - must be licensed, and that any dinghy out on the water must be operated by a Licensed Dinghy Operator (LDO) or an employee of a Competent Dinghy Owner (CDO). CDOs are Goverment organisations such as the Police, Customs, Immigration, Lifeboats and so on. Non-CDO licensing will be done at the local police station, and getting an Operator's licence will require an examination held once a year in a small hall in Clermont-Ferrand Only EU nationals can license a dinghy, and registration must be made by an LDO or the competent applicant (CA) of a CDO. Competent applicants must be company secretaries. Anyone with a Master's Ticket is automatically an LDO. A dinghy must display a license with the name of its LDO / CDO. Oddly, these licence documents will only be available to French organisations: the gendarmerie will always be waiting for those to arrive.

Unlicensed dinghies are subject to immediate confiscation by the French Police. Selling a dinghy to anyone who is not an LDO/CDO is illegal, as is transporting unlicensed dinghies. As you can guess, practically every dinghy not on a ship or used by a government organisation, will be unlicensed.

Now when the French Police see a bunch of people huddled around a dinghy, they can move in, confiscate the dinghy, and leave. No need to ask for anyone's papers. No need to get involved in debates about illegal immigration or anything else. They're just taking the dinghy. And leaving Gaston behind to make sure nobody brings another dinghy out from behind the shed.

If the dinghy does make it into the water, the French can go after it, make them turn around, confiscate the dinghy, and leave everyone else on the shore. Nobody is stopping illegal immigrants illegally immigrating. It's just an administrative law. Nothing personal.