Great Wall of China vs Border Fence

I was doing a little reading on the Great Wall of China today. The thing is actually several walls joined together, and stretches some 4000 miles plus. It was built about 3000 years ago.

So I got to thinking. The ancient Chinese were able to build a 4000 mile wall, but our modern 21st century government can't seem to build a 2000 mile border fence to keep out illegals.
Some experts say the best way to go is to repair the 9-foot high fencing than runs along a portion of the Mexican border and extend it with enough fencing to close-off the entire 1952-mile length of the border. Wanna bet how long it will be before that happens? Think it will be here 3000 years from now? Or even 300? 30? Ever?