Not a bad idea, but I’d prefer no announcement at all. Why should we have to announce that we are going to enforce our laws. I say just do it.
I’d start with the most egregious offenders. Start prosecuting/jailing/deporting the illegal voters, the murderers, the rapists, those illegally on welfare, the frequent fliers in the court system. Make the penalties harsh and make them stick. Work your way down to the lesser offenses. Word will get out.
Making a threat that you can’t make good on (because catching and prosecuting all of them is virtually impossible, a few will always slip through the cracks, also because there are so many that the courts will be overwhelmed) is, IMO, a threat that will be largely ignored. But if they start seeing prosecutions everywhere around them, word of mouth will encourage more to self-deport. In addition, they won’t know who/when/where so the level of uncertainty will also be an advantage in encouraging self-deportation.
Yes, I love your idea. Keep people guessing...On pins and needles.