The easiest way to ensure that would be to get rid of all gasoline-based gas stations and replace them with electric ones. So even if someone tries to sneak in a gas car, they won’t be able to refill it.
That wouldn’t work, there are zillions of existing ICE cars there already in use. They aren’t banning ICE cars that are already there, just banning importation of new ones
Not to mention non-street legal ICE engines, like generators, water pumps or ag equipment. We should be pursing less reliance on fossil fuels, but in the correct order. More EVs means more need for reliable power infrastructure. Then we wouldn’t need generators, irrigation pumps become easier to run from electricity and tractors can be migrated to EV or fueled by biofuels(biogas or biodiesel) to fill the gap.