We don't need to.
Simply make it impossible for them to engage in economic activity (work or the government trough) and they'll throw themselves out.
Exactly, make a mandatory fine of $500k per illegal employee or ones with false/forged documents a business has. Businesses will then do extensive background checks, the illegals will not be able to find jobs and deport themselves. Also immediate termination and prison for any government employee that aids them in obtaining any form of government assistance.
So we don’t need to build a wall?