So it appears that the federal government built a 15-mile-long fence along New Mexico's border with Mexico back in 2000. Recently, however, they realized they'd built 1.5 miles of it about six feet into Mexican territory. From the AP article:
The Mexican government was notified and did what any landowner would do: They sent a note politely insisting that Mexico get its land back.
"Our country will continue insisting for the removal (of the fence) to be done as quickly as possible," the Foreign Relations Department said in a diplomatic missive to Washington.
When the barrier was built in 2000, the project was believed to cost about $500,000 a mile. Estimates to uproot and replace it range from $2.5 million to $3.5 million.(This is today's last post.)