Many of these illegals congregate every day all across the country to get work. And everyday local contractors come around to pick them up. Why not start taking names of contractors off their trucks or license plates. This would be followed up with a warning letter containing a copy of the law and informining them their hiring of potential illegals has been noted.?
Hey, now - Hey now! I rely on those people to clear my yard and other valuable services. Don't be sending me any warning letters!
That's what the Minute Men are doing and they're catching a lot of grief for it.
It would be meaningless, since El Presidente prosecutes no one for hiring illegals. And he would be calling you a vigilante in his next speech.