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The contractors are erecting eight prototypes in San Diego - four made of concrete and four of other materials. Construction will last about 30 days.
U.S. Customs and Border Protection may pick several designs, or none. They agency says in a press release that the designs will inform standards for future construction.
The prototypes will be up to 30 feet high (9 meters high) and 30 feet long.
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Construction is starting three months behind schedule after losing bidders lodged protests that were ultimately unsuccessful.