I could (if given free reign) have the border sealed tight in three months. It just takes the will to do it. Ten miles of fence could easily be built in one day. Predatros with helicopter response teams and roaming patrols with the power to turn back invaders. Add a 50% tax to all money leaving the US and going to Mexico. However, the real solution is to make it very painful to get caught employing an illegal.
Don't forget making it unlawful to supply any welfare benefits, tax credits, social security, unemployment, taxpayer-funded education, or other government benefit to people that are here illegally. Take away the freebies and most will leave on their own.