We can all agree — the President, Republicans and Democrats in Congress, and people all across the country — that we need secure borders. I also agree with the president that having a secure southern border requires physical barriers. The question is: what type of physical barriers are best? And how can technology and surveillance fill the void when physical barriers are not feasible?

I’ve been working on this issue with some of my colleagues for years. The bipartisan immigration reform bill that passed the Senate in 2013 (which I helped author) provided for 700 miles of fencing, including “double fencing” in some areas. This was in addition to doubling the number of border patrol agents from 20,000 to 40,000 as well as providing a host of other technological and border infrastructure improvements and significant additional resources to prosecute illegal border crossers.

Throughout the campaign, President Trump spoke extensively of “building a wall” along the southern border and his first budget asked for funding for “bricks and mortar” for a wall. I understand what he’s trying to accomplish, but there are there better ways to secure the border than a “brick and mortar” wall.

The closest thing we have had to a “wall” along the southern border were the surplus Vietnam War-era “landing mats” that are turned upward and placed end-to-end through some of the border communities. Because border patrol agents couldn’t see what was happening on the other side of the wall, rocks were often thrown over them, causing injury to agents and damage to border patrol vehicles. Consequently, these walls have largely been replaced with fencing.

It’s important to understand what sort of fencing we are talking about. It’s not a short chainlinked fence or a barb-wired fence you’d see on a ranch. We’re talking about a solid steel structure that often rises 20 feet above the ground but has narrow gaps allowing border patrols agents to see through to the other side.

I was pleased that during his visit to Arizona this week, President Trump travelled to the border community of Yuma, where “landing mat” walls have been replaced with fences, to great effect. I would invite the President to visit other stretches of the border in Arizona where walls have been replaced by fences in border communities. I should note that in some remote, mountainous areas, even border fences aren’t feasible because of the landscape. In these spaces, sensors, camera towers, and drone surveillance can help fill the void.

There are other issues with border walls. For example, the San Pedro watershed near the town of Naco in southern Arizona empties northward across the border into Arizona. A brick and mortar border wall would be either be breached during the monsoon season, or it would flood border communities on the Mexican side of the border. Even the current border fences in that region need storm gates to allow debris to escape northward through the border fence after a good rainstorm.

If the “border wall” is simply a metaphor for increased border security, which includes a mix of fencing, sensors, towers and drone surveillance, I strongly support the President. Arizonans have been working on this issue for years, and the downward trend in illegal border crossings over the past few years has been encouraging (owing both to better border security and an improving economy in countries south of our border).

But an actual brick and mortar border wall is not the most effective or efficient way to secure our border and keep Arizona safe.