The how did the provisions get funded?
"Although the 2006 law authorized construction of a fence, Congress initially did not fully appropriate funds for it (see authorization-appropriation process). "Congress put aside $1.4 billion for the fence, but the whole cost, including maintenance, was pegged at $50 billion over 25 years, according to analyses at the time."[10]
A 2017 GAO report noted: "According to CBP, from fiscal year 2007 through 2015, it spent approximately $2.3 billion to deploy border fencing along the southwest border, and CBP will need to spend a substantial amount to sustain these investments over their lifetimes. CBP did not provide a current life-cycle costs estimate to maintain pedestrian and vehicle fencing, however, in 2009 CBP estimated that maintaining fencing would cost more than $1 billion over 20 years."[12]"
Secure Fence Act of 2006 - Wikipedia