I like to see them use forfeiture laws. Like they do for people who sell drugs from cars or try to pick up hookers in their car. The car gets seized. Seize any business that knowingly uses persons ineligible to work in the US. A couple of well publicized seizures would change the landscape OVERNIGHT.
People not involved in business need to realize this: Illegal workers are like nuclear weapons. Once one business starts using them, they all have to use them.
In addition to harsh penalties for the owners. See if they can run a business in prison.