Fences are one answer.
Sorry, but I cannot agree. Fences are a money pit! Why would you want to spend millions to build them, millions to maintain them, millions to blow up the tunnels built under them, and on and on and on. The federal Government knows what it will take to stop it but refuse to do it. Fine businesses who hire them! The only answer. Possibly a system like Canada has where the entire burden is placed on the business who employs them! They are responsible for getting them to Canada and getting them out! Sounds pretty good to me.