Right. If no one know then no one will realize tax dollars are paying for it and not Mexico.
The 5% tariff that Trump threatened to slap on all Mexican imports would have raised $17.3 Billion in taxes. I think that would have paid for the wall rather quickly. Fortunately, the Mexicans decided to help slow the immigrant flow before the tariff was imposed.
https://www.cnbc.com/2019/05/31/how-much-trumps-mexico-tariffs-could-cost-you.html