How to anchor a pony wall on a sub-floor?

Obviously the problem with pony walls or half walls is that the have a huge tendency flex or move. Treat the wall like you would a railing on a deck or set of stairs. There needs to be a very strong base to anchor to. You can have a solid steel wall but the floor will allow it to move. If you cannot find floor joists to anchor to, you need to create a one. For me there is no other way. If there is access from below like a basement that's great. If on the second floor you need to open up the floor and expose the joists and sister 2X6 or greater on the joists or make a header spanning between them( do this every 2-3 feet for the length of the wall). Now you will have a strong base to anchor to. Another trick I learned from a welder is to have 3" angle iron welded at 90 degrees. For a short wall like 4' two will do. Bolt them to the floor with lag bolts, min 3.5" (into the solid base you made or joists) Build your wall around the iron and carriage bolt the frame to the metal. You will have a far superior wall that will barley budge. When building the wall also use large screws. 3" or better. Nails will back out of the studs very easy when pressure is applied. Screws won't.