- Painting (Trump wants it black, not rust).
- Repairing sabotage--quite expensive because you need a crew and access to reweld.
- Maintaining roads for access and electronics. It's not clear to me what sort of electronics are involved and how durable they might be.
- Storm gates to allow storm water to flood arroyos. The gates have to be raised during storm season and monitored for people going underneath them.
- Undermined foundations. Downpours can work to erode dirt from around the foundations, leading to collapse.
The article says DHS isn't providing estimates on the maintenance costs. It has a quote predicting in 20 years or so it will be a rusting relict in the desert.
I can readily believe if and when we get immigration legislation and the situation in the Northern Triangle of Central America settles down Congress won't be eager to appropriate money for maintenance. That fits with one lesson I learned in government--maintenance isn't sexy--it doesn't get management attention, you don't get medals for it, you don't get money or people to do it.