Attached are the appropriations (funding) bills for FY19 for the Department of Defense and for Military Construction that the President has signed and are now officially law. Did a quick search in the pdfs for terms like Mexico, southern, border, wall, and fence but found nothing for border security construction along the Mexican border.

The Energy and Water, Legislative Branch, and Military Construction and Veterans Affairs Appropriations Act, 2019 (H.R. 5895 became Public Law No: 115-244 on 21 Sep 2018)

https://www.congress.gov/115/bills/hr5895/BILLS-115hr5895enr.pdf

The Department of Defense and Labor, Health and Human Services, and Education Appropriations Act, 2019 and Continuing Appropriations Act, 2019 (H.R. 6157 became Public Law No: 115-245 on 28 Sep 2018)

https://www.congress.gov/115/bills/hr6157/BILLS-115hr6157enr.pdf

Here's what the MilCon bill (H. R. 5895—58) authorizes for military construction in FY19 (the monies will be in place and can be used up till 30 Sep 2023 - the long period of time is because it takes quite of bit of time for design, contracting, and construction of anything):

SEC. 125. For an additional amount for the accounts and in

the amounts specified, to remain available until September 30, 2023:

‘‘Military Construction, Army’’, $94,100,000;

‘‘Military Construction, Navy and Marine Corps’’,

$196,850,000;

‘‘Military Construction, Air Force’’, $118,450,000;

‘‘Military Construction, Army National Guard’’,

$22,000,000;

‘‘Military Construction, Air National Guard’’, $54,000,000;

‘‘Military Construction, Army Reserve’’, $23,000,000; and

‘‘Military Construction, Air Force Reserve’’, $84,800,000:

Provided, That such funds may only be obligated to carry out construction projects identified in the respective military department’s unfunded priority list for fiscal year 2019 submitted to Congress: Provided further, That such projects are subject to authorization prior to obligation and expenditure of funds to carry out construction: Provided further, That not later than 30 days after enactment of this Act, the Secretary of the military department concerned, or his or her designee, shall submit to the Committees on Appropriations of both Houses of Congress an expenditure plan for funds provided under this section.

Maybe the Congress has funded some "black" money elsewhere that could be used for the wall/fence/security system.