So, an example. An Italian flies in and they say 'dear mr italian, you need to tell us exactly where your staying, and give us your word that you wont go out for 14days'. Mr italian says 'I'm going to be staying at xyz address and no no no I wont go out'.
The police do not have the ability to put surveillance on every single person that enters the country, they can't manage terrorists half the time.
And in the meantime, mr italian has 35 of his closest friends and family round, infects them and they infect loads of others.
Mental.
The only 3 options I can see, is
A quarantine centre of some sorts for 14days and lockdown enforced
They have the ability to do a test in a couple of hours at the airport, en masse, at off-board
They make the country of origin test everyone on the plane before takeoff and provide some sort of cert like a visa or they can't enter (not a temperature bollocks test, a a proper test)