In the 2000s Spencer gained media attention when he converted his ranch on the Arizona and Mexico border into a hi-tech security zone complete with infrared cameras, aerial drones and motion detectors. Spencer patented  this technology, which he then offered free of charge to the US federal government. In 2001, he started warning of a “Mexican takeover of the southwestern United States,” and made a video titled Immigration: Threatening the Bonds of Our Union, which he delivered to every member of Congress. In 2002 he gave a talk entitled "The Second Mexican-American War" at that year's American Renaissance conference.
- Weigel, David (May 6, 2013). "The Fence Junkies". Slate. Retrieved 20 November 2015.
- US patent 9151855, Glenn Spencer & Michael S. King, "Barrier detection system and method", issued 2015-10-06, assigned to Ardmore Associates, LLC
- "CNN WOLF BLITZER REPORTS". CNN. June 23, 2003. Retrieved 20 November 2015.
- Mears, Bill (April 25, 2012). "High court review of immigration enforcement a tale of opposing views". CNN. Retrieved 20 November 2015.
- In Defense of Western Man: The Fifth American Renaissance Conference
- Tobias, Glen; Foxman, Abraham (2003). "Armed Vigilantes in Arizona" (PDF). Border Disputes. Phoenix, New York: Anti-Defamation League (PDF): 2–5. Retrieved 2010-02-02.
- "Glenn Spencer". Southern Poverty Law Center. Montgomery, AL: Southern Poverty Law Center. 2016-05-19. Retrieved 2016-05-19.
- Berkowitz, Bill; Dobbs, Lou (2006-07-01). "Dubious Guest List". Rome: Inter-Press Service. Archived from the original on October 4, 2009. Retrieved 2010-02-02.