As he has stated time and time again. Apparently the idea of what smuggling the goods across the border in small batches would do to the price of the goods, compared with just paying the tariff, hasn't occurred to him.
Again, Fentanyl and other opiods are currently streaming across the border and we have more wherewithal to stop it than they did.
Also, if you bothered to read the newspaper accounts of the time you would understand that many did not think it possible to stop trade across the borders, and additionally, some Northern ports were going to refuse to collect the tariffs if the Southern ports did not have to do so. They correctly recognized that to collect high tariffs would have put them at a severe trade disadvantage.