There are parts of Texas Land Laws that presume that if a land owner moves his fence inbound of his property lines, that he has given up that property to the other adjoining owner.
This could be road right of way easement, a creek he could not properly fence with water gap fencing or just not proper surveying of property lines.
The courts may rule later that the US succeeded the Rio Grande to the Meskins.
Mexico may later void water usage treaties with the US since we gave up the Rio Grande as a border.
"GOOD fences make good neighbors".
ceded