Prototype designs for a proposed wall along the U.S.-Mexico border could be built in June, U.S. Customs and Border Patrol said recently. While CBP officials would not say how many companies had responded to Friday's formal request for wall designs, published reports said a number of large firms with significant experience in managing large projects had expressed interest. The request for plans covered both a concrete wall and one using other materials, like fencing. Meanwhile, a small company thousands of kilometers away from the border is working with firms that design and build projects in the hope of landing some business from the multi-billion-dollar proposal. Riverdale Mills in Northbridge, Massachusetts, already has supplied tall, high-security fencing that guards 43 kilometers of the 3,000-kilometer border. In a VOA interview, Riverdale CEO Jim Knott said his factory can make steel fence with small openings that make climbing or cutting the structure very difficult. If the joint proposal is accepted, he said, his company can turn out specialized fencing quickly and could expand production with new machinery and employees if necessary. Trump's promise Building a wall to keep illegal immigrants out of the United States was a key promise Donald Trump made as a presidential candidate. Approximately one-third of the border already has an assortment of fences or walls. However, many areas, particularly in remote, thinly populated regions, lack such structures. The new wall is generally supposed to be 9 meters tall, block tunneling efforts nearly 2 meters below ground and be "esthetically pleasing" from the U.S. side. The specifications also call for gates that can admit vehicles, and for the structure to be able to withstand at least an hour of efforts to break through it with sledgehammers, welding torches and other common tools. Estimates of the cost to build the wall range from $8 billion to more than $20 billion. Critics of the wall project express concern about its cost, say it could hurt commerce in the border areas of the United States and cause environmental problems. Critics also say that many people who are in the United States illegally arrived by plane legally and then overstayed their visas, a problem that would not be addressed by a wall. Trump has said he will get Mexico to pay for the wall, an idea that Mexican officials have rejected.