How do we "seal" 22,000 miles of border?
22,000 miles? The land border of the US is 12034 km (or 7478 miles), including the Alaska - Yukon border. Add a coastline of 19,924 km (or 12380 miles), and you get up to 19858 miles. The Coast Guard does a decent job of patrolling the coasts already.
CIA World Factbook
Checkpoints every few miles on every highway?
No. Just 1 (one) per highway - at the border.
So maybe I'm off by a little. Whatever.
I was in the USCG for a time... we estimated that we caught about 2% of the illegal traffic into the country. Maybe that's good enough to "seal" those borders. All we need is to be 50 times more effective.
The entire USCG is still smaller than the NYPD.
Some illegals will *always* get past the border. The only way to catch them is to put checkpoints in place all over the country.