While the proposed border wall faces several hurdles, not least of which is obtaining funding for the wall's construction, there is another challenge that may test how far the government is willing to go to build this contentious wall across the border — the private land that lies between the U.S. and Mexico.

The government owns about one-third of the nearly 2,000 miles that make up the border. If the federal government chooses to step in and declare eminient domain to take over that property, it could be a long, complicated process that faces almost certain legal challenges, Curbed reports.

In Texas, wealthy landowners have ranches, golf courses and orchards along border property, with some of those properties going back generations as far as Spanish land grants. But the state's attorney general has stated he has no problem with the use of eminent domain for the wall. Where the border passes through Native American lands there will be additional challenges, such as in Arizona, where the Tohono O'odham Nation has called for protests against any wall that would pass through its lands.

The Department of Homeland Security already has started to make bids for property along the border, sending notices to property owners. Owners can ask for a trial.

Past attempts to secure border property have been met with resistance. Efforts in 2006 to build a border fence yielded lengthy court battles and cost the federal government more than $78M for 654 miles, CNN reports. Another $25M will likely be paid for legal expenses and to settle unresolved real estate transactions.